Interaction of nicotinic and histamine H(3) systems in the radial-arm maze repeated acquisition task.

Nicotinic systems have been found in a variety of studies to play important roles in cognitive function. Nicotinic involvement in different aspects of cognitive function such as learning vs. memory may differ. We have found in rats that the spatial repeated acquisition task in the radial-arm maze is significantly improved by low doses of the nicotinic receptor antagonist mecamylamine, the atypical nicotinic receptor ligand lobeline, as well as the alpha7 nicotinic receptor agonist ARR-17779. Interestingly, nicotine in the same dose range that improves working memory in the win-shift radial maze task was not effective in improving repeated acquisition performance. Nicotinic systems interact with a variety of other neural systems. Differential involvement of these extended effects with learning vs. memory may help explain differential effects of nicotinic drugs with these cognitive functions. Histamine H(3) receptor antagonists have been shown by some studies to improve cognitive function, but others have not found this effect and some have found impairment. Nicotine stimulates the release of histamine. This effect may counter other cascading effects of nicotine in the performance of learning and memory tasks. A specific test of this hypothesis involves our study of nicotine (0.1-0.4 mg/kg) interactions with the histamine H(3) receptor antagonist thioperamide (2.5-10 mg/kg) on learning memory in the repeated acquisition test in the radial-arm maze. The highest dose of thioperamide tested caused a significant choice accuracy impairment, which was most evident during the later portions of the learning curve. The highest dose of nicotine did not change overall errors but did cause a significant impairment in learning over trials. The choice accuracy impairment induced by thioperamide was significantly attenuated by nicotine (0.4 mg/kg). The learning impairment caused by the highest dose of nicotine was significantly attenuated by thioperamide. Thioperamide also caused a slowing of response, an effect, which was attenuated by nicotine co-administration. The repeated acquisition test can help differentiate acute drug effects on learning. Nicotine and thioperamide effectively reversed each other's choice accuracy impairment even though each by itself impaired accuracy.

Current issues in clinical equivalence trials.

A clinical trial designed to show that an experimental treatment E is similar to a control treatment S in a specified direction is a one-sided equivalence or similarity trial--in the terminology of the International Conference on Harmonisation, a non-inferiority trial (ICH, 1998). We design such a study to show that E is not worse than S (often an accepted or standard treatment) by as much as a pre-specified margin theta0. The quantity theta0 can be either a difference or ratio of an appropriate outcome in individuals treated with E and S. A critical issue is whether one can conclude from a non-inferiority trial that E is effective. Closely related is an appropriate choice of theta0, which should be substantially less than the estimated effect of S if available from previous studies; theta0 should also be acceptable to clinicians, either because of advantages of E or because a difference or ratio less than theta0 is considered unimportant clinically. Another possible approach for showing that E is effective is to estimate its effect compared with placebo from historical data. If previous studies that consistently show an effect of S are not available, alternative study designs should be considered. Findings of superiority or non-inferiority of E, when the study was planned to show the other, are possible and may be supportable. A finding that E is at the same time statistically significantly worse than S and "non-inferior" to S should not be a problem, if the criterion theta0 is appropriate and this possibility was considered in the protocol. Various sorts of non-adherence may make treatments appear similar, even if they are not. In particular, random non-adherence of study participants to the assigned treatment regimen may cause an intention-to-treat analysis to give a misleading result of similarity. Thus, maintaining a high degree of adherence to protocol is especially important in an equivalence or non-inferiority trial. Interim analysis does not present statistical problems in these trials; early stopping may not be wise in many cases, however, because strong interim evidence for non-inferiority may actually be an indicator that E is superior to S.

Behavioral alterations in adolescent and adult rats caused by a brief subtoxic exposure to chlorpyrifos during neurulation.

The widely used organophosphate insecticide, chlorpyrifos (CPF), elicits neurobehavioral abnormalities after apparently subtoxic neonatal exposures. In the current study, we administered 1 or 5 mg/kg/day of CPF to pregnant rats on gestational days 9-12, the embryonic phase spanning formation and closure of the neural tube. Although there were no effects on growth or viability, offspring showed behavioral abnormalities when tested in adolescence and adulthood. In the CPF-exposed groups, locomotor hyperactivity was noted in early T-maze trials, and in the elevated plus-maze; alterations in the rate of habituation were also identified. Learning and memory were adversely affected, as assessed using the 16-arm radial maze. Although all CPF-exposed animals eventually learned the task, reference and working memory were impaired in the early training sessions. After training, rats in the CPF group did not show the characteristic amnestic effect of scopolamine, a muscarinic acetylcholine antagonist, suggesting that, unlike the situation in the control group, muscarinic pathways were not used to solve the maze. These results indicate that apparently subtoxic CPF exposure during neurulation adversely affects brain development, leading to behavioral anomalies that selectively include impairment of cholinergic circuits used in learning and memory. The resemblance of these findings to those of late gestational or neonatal CPF exposure indicates a prolonged window of vulnerability of brain development to CPF.

Learning impairment caused by a toxin produced by Pfiesteria piscicida infused into the hippocampus of rats.

Pfiesteria piscicida, an estuarine dinoflagellate, which has been shown to kill fish, has also been associated with neurocognitive deficits in humans. With a rat model, we have demonstrated the cause-and-effect relationship between Pfiesteria exposure and learning impairment. In several studies, we have replicated the finding in Sprague-Dawley rats that exposure to fixed acute doses of Pfiesteria cells or filtrates caused radial-arm maze learning impairment. Recently, this finding of Pfiesteria-induced learning impairment in rats has been independently replicated in another laboratory as well. We have demonstrated significant Pfiesteria-induced learning impairment in both the win-shift and repeated-acquisition tasks in the radial-arm maze and in reversal learning in a visual operant signal detection task. These learning impairments have been seen as long as 10 weeks after a single acute exposure to Pfiesteria. In the current study, we used a hydrophilic toxin isolated from clonal P. piscicida cultures (PfTx) and tested its effect when applied locally to the ventral hippocampus on repeated acquisition of rats in the radial-arm maze. Toxin exposure impaired choice accuracy in the radial-arm maze repeated acquisition procedure. The PfTx-induced impairment was seen at the beginning of the session and the early learning deficit was persistent across 6 weeks of testing after a single administration of the toxin. Eventually, with enough practice, in each session, the PfTx-exposed rats did learn that session's problem as did control rats. This model has demonstrated the cause-and-effect relationship between exposure to a hydrophilic toxin produced by P. piscicida and learning impairment, and specifically that the ventral hippocampus was critically involved.

Effect of rotavirus vaccination programme on trends in admission of infants to hospital for intussusception.

BACKGROUND: Studies have reported a temporal association between a first dose of rotavirus vaccine (Rotashield) and infant intussusception. We investigated the effect of Rotashield vaccination use on intussusception admissions in ten US states. METHODS: We analysed electronic databases containing 100% hospital discharge records for 1993-99 from ten US states, where an estimated 28% of the birth cohort had received Rotashield (based on manufacturer's net sales data). We examined records of infants admitted to hospital (<365 days old) with any mention of intussusception (International Classification of Diseases, ninth revision, clinical modification code 560.0). Excess admissions for intussusception during the period of Rotashield availability (October 1998 to June 1999) were estimated by direct comparison with the corresponding period of October 1997 to June 1998 (before Rotashield was available) and with adjustment for secular trends during 1993-98 by Poisson regression. FINDINGS: Hospital admission for intussusception among infants younger than 365 days of age during the Rotashield period compared with previously was 4% lower (10 cases) by direct comparison and 10% lower (27 cases) by trend comparison, corresponding to a negative population attributable risk. Among infants aged 45-210 days (target age range for a first Rotashield dose), we estimated an increase in intussusception admissions of 1% (one excess admission) by direct comparison and 4% (4.6 excess admissions) by trend comparison, corresponding to a population attributable risk range of one excess admission in 66000-302000. INTERPRETATION: We found no evidence of increased infant intussusception admissions during the period of Rotashield availability. The total intussusception admission risk attributable to Rotashield was substantially lower than previous estimates based on studies focusing on the immediate postvaccination weeks.

Allocation of subjects to test null relative risks smaller than one.

Allocating a proportion k'=1/(1+ radicalr(0)) of subjects to an intervention is a practical approach to approximately maximize power for testing whether an intervention reduces relative risk of disease below a null ratio r(0)<1. Furthermore, allocating k'(s), a convenient fraction close to k', to intervention performs nearly as well; for example, allocating k'(s)=3/5 for 0.5> or =r(0)>0.33,2/3 for 0.33> or =r(0)>0.17 and 3/4 for 0.17> or =r(0)> or =0.10. Both k' and k'(s) are easily calculated and invariant to alterations in disease rate estimates under null and alternative hypotheses, when r(0) remains constant. In examples that we studied, allocating k' (or k'(s)) subjects to intervention achieved close to the minimum possible sample size, given test size and power (equivalently, maximum power, given test size and sample size), for likelihood score tests. Compared to equal allocation, k' and k'(s) reduced sample sizes by amounts ranging from approximately 5.5 per cent for r(0)=0.50 to approximately 24 per cent for r(0)=0.10. These sample size savings may be particularly important for large studies of prophylactic interventions such as vaccines. While k' was derived from variance minimization for an arcsine transformation, we do not recommend the arcsine test, since its true size exceeded the nominal value. In contrast, the true size for the uncorrected score test was less than the nominal size. A skewness correction made the size of the score test very close to the nominal level and slightly increased power. We recommend using the score test, or the skewness-corrected score test, for planing studies designed to show a ratio of proportions is less than a prespecified null ratio r(0)<1.

Importance of complement source in measuring meningococcal bactericidal titers.

Complement-mediated bactericidal antibodies in serum confer protection against meningococcal disease. The minimum protective titer is estimated to be between 1:4 and 1:8 when measured by the Goldschneider assay performed with human complement, the assay used in the 1960s to establish the correlation between bactericidal antibodies and protection. A more recently described bactericidal assay standardized by an international consortium uses rabbit complement, which is known to augment bactericidal titers. To define a protective titer measured by the standardized assay, we compared bactericidal titers against serogroup C strains measured by this assay to titers measured by the assay described by Goldschneider et al. A titer of > or =1:128 measured by the standardized assay was needed to predict with > or =80% certainty a positive titer of > or =1:4 as measured by the Goldschneider assay. However, the majority of samples with titers of 1:4 measured by the Goldschneider assay had titers of <1:128 when measured by the standardized assay. Therefore, by the results of the standardized assay such persons would be falsely categorized as being susceptible to disease. In conclusion, high bactericidal titers measured with the standardized assay performed with rabbit complement are predictive of protection, but no threshold titer is both sensitive and specific for predicting a positive titer measured by the Goldschneider assay using human complement. Up to 10% of the U.S. adult population lacks intrinsic bactericidal activity against serogroup C strains in serum and can serve as complement donors. Therefore, use of the Goldschneider assay or an equivalent assay performed with human complement is preferred over assays that use rabbit complement.

Safety and immunogenicity of a recombinant hemagglutinin vaccine for H5 influenza in humans.

Recent outbreaks of avian influenza in humans have demonstrated the need for vaccines for influenza viruses with pandemic potential. Recombinant hemagglutinins are an attractive option for such vaccines because they do not require handling potentially highly pathogenic influenza viruses for vaccine production. In order to evaluate the immunogenicity, optimum dosing and timing of administration of a recombinant baculovirus-expressed H5 HA (rH5) in humans, 147 healthy adults were assigned randomly to receive intramuscular rH5 as two doses of 25, 45 or 90 microg each, one dose of 90 microg followed by a dose of 10 microg, or two doses of placebo, at intervals between doses of 21, 28 or 42 days. All doses of rH5 were well tolerated. The rH5 vaccine was modestly immunogenic at high dose. Neutralizing antibody responses to a titer of 1:80 or greater were seen in 23% (14/60) of individuals after a single dose of 90 microg, and in 52% (15/29) after two doses of 90 microg. Varying intervals between doses from 21 to 42 days had no significant effect on antibody responses to vaccination. These results suggest that baculovirus-expressed H5 HA can induce functional antibody in individuals who have not had prior exposure to H5 viruses, but that further studies to improve the immunogenicity of the vaccine are needed.

Decreased bone mineral density during low dose glucocorticoid administration in a randomized, placebo controlled trial.

OBJECTIVE: While osteoporosis and bone fractures are clearly recognized side effects of high dose glucocorticoids, the effect of low dose glucocorticoids remains controversial. We investigated the effect of 3 months of low dose hydrocortisone on bone mineral density (BMD). METHODS: Subjects, 18 to 55 years old with chronic fatigue syndrome and no medical or psychiatric illness requiring medication, were randomized in a double blind, placebo controlled trial to receive oral hydrocortisone, 13 mg/m2 body surface area every morning and 3 mg/m2 every afternoon (25 to 35 mg/day, equivalent to about 7.5 mg prednisone/day) or placebo for 12 weeks. Before and after treatment BMD of the lumbar spine was measured by dual energy x-ray absorptiometry. RESULTS: We studied 23 subjects (19 women, 4 men). For the 11 hydrocortisone recipients there was a mean decrease in BMD: mean change from baseline of the lateral spine was -2.0% (95% CI -3.5 to -0.6. p = 0.03) and mean change of the anteroposterior spine was -0.8% (95% CI -1.5 to -0.1, p = 0.06). Corresponding changes for the 12 placebo recipients were +1.0% (95% CI -1.0 to 3.0, p = 0.34) and +0.2% (95% CI -1.4 to 1.5, p = 0.76). CONCLUSION: A 12 week course of low dose glucocorticoids given to ambulatory subjects with chronic fatigue syndrome was associated with a decrease in BMD of the lumbar spine. This decrease was statistically significant in lateral spine measurements and nearly so in anteroposterior spine measurements.

Safety and immunogenicity of six acellular pertussis vaccines and one whole-cell pertussis vaccine given as a fifth dose in four- to six-year-old children.

OBJECTIVE: To evaluate the safety and immunogenicity of 6 different acellular pertussis vaccines combined with diphtheria and tetanus toxoids (DTaP) and with 1 licensed whole-cell pertussis vaccine (DTwP) as a fifth dose in children who had previously received the same DTaP, a different DTaP, or DTwP as primary and fourth-dose vaccinations. METHODS: Healthy 4- to 6-year-old children were enrolled at 5 National Institute of Allergy and Infectious Diseases Vaccine Treatment and Evaluation Units to receive a fifth dose of a DTaP or DTwP vaccine. All had been randomly assigned to receive 3 primary doses of DTaP or DTwP at 2, 4, and 6 months and a fourth-dose booster at 15 to 20 months of age as part of earlier National Institutes of Health multicenter acellular pertussis vaccine trials. Parents recorded the occurrence and magnitude of fever, irritability, and injection site redness, swelling, and pain for 3 days after vaccination. Sera obtained before and 1 month after the booster vaccination were analyzed by enzyme-linked immunosorbent assay for antibody to pertussis toxin, filamentous hemagglutinin, fimbriae, pertactin, and diphtheria and tetanus toxoid. Safety and/or immunogenicity data are reported for 317 children who received DTaP and 10 children who received DTwP. RESULTS: Fever and moderate or severe irritability were uncommon following the fifth dose of DTaP vaccine and were generally less frequent than following the fourth dose. However, for the DTaP vaccine groups, redness, swelling, and pain increased in prevalence compared with the fourth dose. The time course and frequency of reactions following DTaP vaccination were generally similar in children who received the same DTaP, a different DTaP, or DTwP for previous doses in the 5- dose series. No significant differences among the DTaP vaccines were detected in the occurrence of reactions, but the statistical power to detect differences was limited by sample size. Significant increases in antibodies directed against the included antigens were observed for all DTaP vaccines in paired pre- and post-fifth dose sera. Post-fifth dose antibody concentrations differed significantly among the DTaP vaccines. Some children in the study showed an antibody response to an antigen not reported to be in the DTaP vaccine. CONCLUSION: All the studied DTaP vaccines performed similarly with regard to reactions, whether given as a fifth sequential dose of the same vaccine, a mix of different DTaP vaccines in the 5-dose sequence, or after 3 DTwP and 1 DTaP vaccinations. Large injection site reactions occurred more frequently after the fifth dose of DTaP than after the previous 4 doses. A fifth dose of all DTaP vaccines induced an antibody response to those antigens contained in the vaccine. No DTaP was consistently most or least reactogenic or immunogenic.

Low-dose hydrocortisone for treatment of chronic fatigue syndrome: a randomized controlled trial.

CONTEXT: Chronic fatigue syndrome (CFS) is associated with a dysregulated hypothalamic-pituitary adrenal axis and hypocortisolemia. OBJECTIVE: To evaluate the efficacy and safety of low-dose oral hydrocortisone as a treatment for CFS. DESIGN: A randomized, placebo-controlled, double-blind therapeutic trial, conducted between 1992 and 1996. SETTING: A single-center study in a tertiary care research institution. PATIENTS: A total of 56 women and 14 men aged 18 to 55 years who met the 1988 Centers for Disease Control and Prevention case criteria for CFS and who withheld concomitant treatment with other medications. INTERVENTION: Oral hydrocortisone, 13 mg/m2 of body surface area every morning and 3 mg/m2 every afternoon, or placebo, for approximately 12 weeks. MAIN OUTCOME MEASURES: A global Wellness scale and other self-rating instruments were completed repeatedly before and during treatment. Resting and cosyntropin-stimulated cortisol levels were obtained before and at the end of treatment. Patients recorded adverse effects on a checklist. RESULTS: The number of patients showing improvement on the Wellness scale was 19 (54.3%) of 35 placebo recipients vs 20 (66.7%) of 30 hydrocortisone recipients (P =.31). Hydrocortisone recipients had a greater improvement in mean Wellness score (6.3 vs 1.7 points; P=.06), a greater percentage (53% vs 29%; P=.04) recording an improvement of 5 or more points in Wellness score, and a higher average improvement in Wellness score on more days than did placebo recipients (P<.001). Statistical evidence of improvement was not seen with other self-rating scales. Although adverse symptoms reported by patients taking hydrocortisone were mild, suppression of adrenal glucocorticoid responsiveness was documented in 12 patients who received it vs none in the placebo group (P<.001). CONCLUSIONS: Although hydrocortisone treatment was associated with some improvement in symptoms of CFS, the degree of adrenal suppression precludes its practical use for CFS.

Human papillomavirus, anal squamous intraepithelial lesions, and human immunodeficiency virus in a cohort of gay men.

Cross-sectional associations between human papillomavirus (HPV), anal squamous intraepithelial lesions (SIL), and human immunodeficiency virus (HIV) were studied in a cohort of gay men. HPV DNA was detected by generic and type-specific polymerase chain reaction (PCR) probes and hybrid capture assay (HC). HPV virus load was estimated by HC relative light unit (RLU) ratio. HPV prevalence, number of HPV types detected, and HC RLU ratios were each greater in HIV-positive than HIV-negative participants. Further, among HIV-positive men, HC RLU ratio was inversely associated with CD4 cell count. SIL was more frequent in HIV-positive participants, particularly those with a CD4 cell count <200/microL and was positively associated with HPV. Men with a high HC RLU ratio were nearly 3 times more likely to have SIL than were those both PCR- and HC-negative. These data support that HIV augments HPV-associated anal disease in this population.

Estimation of pertussis vaccine efficacy in the presence of covariates in three randomized trials.

We estimated efficacy of pertussis vaccines in three randomized controlled trials with adjustment for several baseline covariates: presence of one or more other children in the household, sex of the study child, and geographical area. Adjusted and unadjusted efficacy estimates differed only trivially. We also assessed the association of efficacy with time since vaccination and background pertussis incidence. The acellular vaccines, except for the two-component vaccine in the Stockholm trial, appeared to maintain their efficacy during two years of follow-up. In contrast, efficacy of a whole-cell vaccine decreased significantly in both the Stockholm and Italian trials. The relationship between efficacy and background incidence was not consistent across studies and vaccines.

Colonization with group B streptococci in pregnancy and adverse outcome. VIP Study Group.

OBJECTIVE: Our purpose was to study the association of cervicovaginal colonization with group B streptococci with pregnancy and neonatal outcome. STUDY DESIGN: A prospective study was conducted at seven medical centers between 1984 and 1989. Genital tract cultures were obtained at 23 to 26 weeks' gestation and at delivery. Prematurity and neonatal sepsis rates were compared between group B streptococci positive and negative women. RESULTS: Group B streptococci was recovered from 2877 (21%) of 13,646 women at enrollment. Heavy colonization was associated with a significant risk of delivering a preterm infant who had a low birth weight (odds ratio = 1.5, 95% confidence interval 1.1 to 1.9). Heavily colonized women given antibiotics effective against group B streptococci had little increased risk of a preterm, low-birth-weight birth. Women with light colonization were at the same risk of adverse outcome as the uncolonized women. Neonatal group B streptococci sepsis occurred in 2.6 of 1000 live births in women with and 1.6 of 1000 live births in women without group B streptococci at 23 to 26 weeks' gestation (p = 0.11). However, sepsis occurred in 16 of 1000 live births to women with and 0.4 of 1000 live births to women without group B streptococci at delivery (p < 0.001). CONCLUSIONS: Heavy group B streptococci colonization of 23 to 26 weeks' gestation was associated with an increased risk of delivering a preterm, low-birth-weight infant. Cervicovaginal colonization with group B streptococci at 23 to 26 weeks' gestation was not a reliable predictor of neonatal group B streptococci sepsis. Colonization at delivery was associated with sepsis.

A controlled trial of two acellular vaccines and one whole-cell vaccine against pertussis. Progetto Pertosse Working Group.

BACKGROUND: Concern about both safety and efficacy has made the use of whole-cell pertussis vaccines controversial. In some European countries, including Italy, the rate of vaccination against pertussis is low. METHODS: We conducted a double-blind trial in Italy in which infants were randomly assigned to vaccination at two, four, and six months of age with an acellular pertussis vaccine together with diphtheria and tetanus toxoids (DTP); a DTP vaccine containing whole-cell pertussis (manufactured by Connaught Laboratories); or diphtheria and tetanus toxoids without pertussis (DT). The acellular DTP vaccine was either one containing filamentous hemagglutinin, pertactin, and pertussis toxin inactivated with formalin and glutaraldehyde (SmithKline Beecham) or one with filamentous hemagglutinin, pertactin, and genetically detoxified pertussis toxin (Chiron Biocine). Pertussis was defined as 21 days or more of paroxysmal cough, with infection confirmed by culture or serologic testing. RESULTS: The efficacy of each vaccine, given in three doses, against pertussis was determined for 14,751 children over an average of 17 months, with cases included in the analysis if cough began 30 days or more after the completion of immunization. For both of the acellular DTP vaccines, the efficacy was 84 percent (95 percent confidence intervals, 76 to 89 percent for Biocine DTP and 76 to 90 percent for SmithKline DTP), whereas the efficacy of the whole-cell DTP vaccine was only 36 percent (95 percent confidence interval, 14 to 52 percent). The antibody responses were greater to the acellular vaccines than to the whole-cell vaccine. Local and systemic adverse events were significantly more frequent after the administration of the whole-cell vaccine. For the acellular vaccines, the frequency of adverse events was similar to that in the control (DT) group. CONCLUSIONS: The two acellular DTP vaccines we studied were safe, immunogenic, and efficacious against pertussis, whereas the efficacy of the whole-cell DTP vaccine was unexpectedly low.

A placebo-controlled trial of a pertussis-toxoid vaccine.

BACKGROUND: Although many whole-cell vaccines have been effective in preventing pertussis, these vaccines are difficult to standardize and can produce side effects. In Sweden, pertussis became endemic during the 1970s despite vaccination. Because of its limited efficacy, the Swedish-made whole-cell vaccine was withdrawn in 1979. METHODS: To evaluate the efficacy of an acellular vaccine consisting of pertussis toxin inactivated by hydrogen peroxide (pertussis toxoid), we conducted a randomized, double-blind, placebo-controlled trial in Sweden. Infants were vaccinated with either diphtheria and tetanus toxoids alone (DT toxoids, 1726 infants) or diphtheria, tetanus, and pertussis toxoids (DTP toxoids, 1724 infants) at 3, 5, and 12 months of age. RESULTS: There were no serious reactions. With the pertussis vaccine there were slightly more local reactions than with the DT toxoids alone, but the rates of postvaccination fever were the same. The main period of surveillance, which began 30 days after the third vaccination, continued for a median of 17.5 months. There were 312 cases of pertussis (72 in the DTP-toxoids group and 240 in the DT-toxoids group) that met the clinical criterion (paroxysmal cough lasting > or = 21 days) and laboratory criteria for pertussis as defined by the World Health Organization. The efficacy of this acellular vaccine was 71 percent (95 percent confidence interval, 63 to 78 percent). The recipients of DTP toxoids who had pertussis had cough of shorter duration than the recipients of DT toxoids, and fewer had whooping and vomiting. The vaccine efficacy after two doses was 55 percent (95 percent confidence interval, 12 to 78 percent), on the basis of 14 cases in the DTP-toxoids group and 31 in the DT-toxoids group that met the definition of the World Health Organization. CONCLUSIONS: A pharmacologically inert, acellular pertussis-toxoid vaccine that is easily standardized is safe and confers substantial protection against pertussis.

Association of reactions after consecutive acellular or whole-cell pertussis vaccine immunizations.

OBJECTIVE: To evaluate the relative frequency of adverse reactions after initial and subsequent immunizations among infants receiving primary immunization with acellular (DTaP) or whole-cell (DTP) pertussis vaccine with diphtheria and tetanus combined. METHODS: We examined the occurrence of common reactions in 2127 infants within 48 hours after immunization at 2, 4, and 6 months with one of 13 DTaP or with Lederle DTP (WCL). Data on at least two consecutive immunizations were available for 357 WCL recipients and 1770 DTaP recipients. For these analyses, reactions evaluated included fever of 100.4 degrees F (38 degrees C) or greater, redness of 21 mm or larger, swelling of 21 mm or larger, moderate or severe pain, moderate or severe fussiness, loss of appetite, drowsiness, and vomiting. RESULTS: With one exception, reactions were approximately 1.5 to 8 times more likely to occur in WCL recipients if the same reaction had been observed at the previous immunization (the single exception was redness after the second immunization). Both initial and repeated reactions were less likely in DTaP than in WCL recipients. As with WCL recipients, risks of repeated reactions in DTaP recipients were higher than the risks of initial reactions (from 2.5 to 24 times as high). CONCLUSION: Reactions after a second or third immunization with either WCL or DTaP vaccine are more likely to occur in infants who had the same reaction after the preceding immunization. Absolute risks of repeated reactions tended to be lower after DTaP vaccine than after the WCL vaccine.

Comparison of five calculation modes for antibody ELISA procedures using pertussis serology as a model.

During a phase III pertussis vaccine trial, serum antibody responses were measured by two enzyme-linked immunosorbent assays (ELISA) for pertussis toxin and filamentous haemagglutinin. These were used both for studies of antibody levels after vaccination and for diagnostic purposes. Since the absorbance values obtained were not directly proportional to the amount of antibody in the samples, ELISA optical densities were transformed to units by calibration to a reference serum. Five different calculation modes were compared. In four of these modes unit calculations were based on the relationship between dose response curves of the serum sample and a reference serum. In addition, traditional endpoint titres were included in the comparison. The calculation mode using reference line units showed the highest reproducibility, with intrassay coefficients of variation (CV) within the same test plate of 4-7% and interassay CVs of 12-14%. The CVs among the other methods ranged from 6 to 31% for intra-assay comparisons and from 12 to 47% for interassay comparisons. Furthermore, the CV values for intra-assay variations were used to calculate standardized differences between 79 pairs of acute and convalescent sera from cases confirmed by culture. These differences were then used to estimate the 'diagnostic sensitivity' for the different calculation modes. The results indicated that use of the reference line units was the most sensitive, whereas use of the end point titers was the least sensitive of these calculation modes.

Similarity/equivalence trials for combination vaccines.

In a similarity or "equivalence" trial of a combination vaccine, we wish to show that the combination is sufficiently similar to the separately administered components in some measure of safety, immunogenicity, or efficacy to justify use of the combination. In this setting it is usually required to show similarity in one direction only; specifically, we design the trial to rule out superiority of the separate components by as much as a prespecified quantity theta 0 in an appropriate outcome measure (e.g., a difference or ratio). It is crucial that theta 0 be chosen to be clinically meaningful, so that any difference or ratio less than theta 0 is truly acceptable to clinicians. Estimation is generally more relevant than hypothesis testing in such a trial, and consequently it is natural to consider design and analysis in terms of confidence intervals. The same sample sizes can be obtained, however, from a hypothesis testing approach. The appropriate null hypothesis is that the separate components are superior to the combination by at least theta 0, with rejection of the hypothesis supporting a conclusion of similarity. It is not appropriate to design the trial to test the null hypothesis of no difference, as we would do if we wished to demonstrate superiority of the combination vaccine; failure to reject that hypothesis does not prove similarity, and we might reject the hypothesis when the true difference is unimportant clinically. Further, this inappropriate approach may result in a sample size either larger or smaller than necessary. Sample size formulations are available for various types of comparative measures, e.g., a difference of normally distributed means, a difference or ratio of proportions, and a ratio of hazards.

Outcome of the Vaginal Infections and Prematurity Study: results of a clinical trial of erythromycin among pregnant women colonized with group B streptococci.

OBJECTIVE: Our purpose was to determine whether erythromycin treatment of pregnant women colonized with group B streptococci would reduce the occurrence of low birth weight (< 2500 gm) and preterm (< 37 completed weeks) birth. STUDY DESIGN: In a double-blind clinical trial, 938 carriers of group B streptococci were randomized to receive erythromycin base (333 mg three times a day) or matching placebo beginning during the third trimester and before 30 weeks and continuing for 10 weeks or until 35 weeks 6 days of pregnancy. RESULTS: Pregnancy outcomes were available for 97% of randomized women; 14% of subjects withdrew from the trial. Birth weight < 2500 gm occurred in 8.6% of the erythromycin and 6.1% of the placebo recipients (relative risk 1.4, 0.9 to 2.2, p = 0.16). Preterm delivery occurred in 11.4% of women randomized to erythromycin and in 12.3% randomized to placebo (relative risk 0.9, 95% confidence limits 0.6 to 1.3, p = 0.65). Greater benefit of erythromycin in reducing these outcomes was not observed among women reporting the best compliance. CONCLUSIONS: In this study of pregnant women colonized with group B streptococci treatment with erythromycin was not shown to be effective at prolonging gestation or reducing low birth weight. Greater than anticipated complicating factors, including spontaneous clearance of the organism, use of nontrial antibiotics, and density of colonization, may have resulted in population sizes too small to detect a benefit of treatment. Future studies should take these factors into account in determining sample sizes.