Experimental gonococcal urethritis and reinfection with homologous gonococci in male volunteers.

BACKGROUND: Reinfection, a common occurrence with gonorrhea, may result from a lack of protective immune response, or from the tremendous gonococcal strain variation. GOAL: A two-phase study in human volunteers tested whether experimental infection with Neisseria gonorrhoeae MS11mkC would protect against reinfection with the same organisms. STUDY DESIGN: In phase 1, an intraurethral inoculum of 57,000 piliated, transparent (opacity protein-negative [Opa-]) MS11mkC N gonorrhoeae infected 14 of 15 (93%) volunteers. The volunteers were encouraged to delay treatment for at least 5 days. In phase 2, which began 2 weeks after treatment for the initial infection, volunteers were inoculated with 7,100 piliated, Opa- MS11mkC. RESULTS: The phase 2 challenge infected 6 of 14 (43%) previously infected volunteers and 5 of 10 (50%) naïve control subjects. Phase 1 volunteers who resisted reinfection were significantly more likely to have had a fourfold or greater increase in lipooligosaccharide immunoglobulin G during phase 1 than those who did not resist reinfection (P = 0.026). CONCLUSIONS: Although infection did not provide protection from reinfection under the conditions used, the results suggest that immunity to reinfection is more complex than anticipated by the experimental design.

Large scale safety study of a liquid hexavalent vaccine (D-T-acP-IPV-PRP--T-HBs) administered at 2, 4, 6 and 12-14 months of age.

A study was conducted to assess the safety of a new, liquid hexavalent vaccine (Hexavac, Aventis Pasteur MSD, Lyon, France) in a large population of 1783 children in Germany vaccinated at 2, 4, 6 and 12-14 months of age. Immediate reactions, local and systemic reactions, and serious adverse events (SAEs) were monitored. The frequencies of redness > or = 2 cm and swelling > or = 2 cm were 6.7 and 7.1% after all doses of the primary series combined and 13.4 and 12.0% following the booster dose, respectively. Transient swelling of the entire thigh was reported in seven infants after all doses of the primary series (0.1%) and in four children after the booster dose (0.2%). The most frequent systemic adverse events within 3 days after vaccination were irritability (19.3% after primary series and 13.2% after booster) and fever > or = 38.0 degrees C (15.4% after primary series and 28.5% after booster). Fever above 40.0 degrees C was reported in 0.1% of the infants post-primary series and in 0.9% of the children after the booster immunization. Only 3 of 144 SAE were considered to be vaccine related and were seen to resolve spontaneously and without sequelae. The liquid hexavalent vaccine was generally well tolerated when given to children as a primary immunization series at 2, 4 and 6 months and as a booster dose at 12-14 months.

The effectiveness of Haemophilus influenzae type b conjugate vaccines in a high risk population measured using immunization register data.

The Northern Territory of Australia has had historically very high incidence rates of invasive Haemophilus influenzae type b disease in children less than 5 years of age, with the burden of disease greatest among Aboriginal infants less than 12 months. This study documents the impact of conjugate Hib vaccines introduced in 1993. Immunization rates were monitored using an existing immunization register, and case finding was done retrospectively using hospital and laboratory records. Following the vaccine introduction, the incidence fell abruptly to a seventh of its pre-vaccination level, in both Aboriginal and non-Aboriginal children. The effectiveness of PRP-OMPC (PedvaxHIB) was 97.5% and the overall effectiveness of the vaccination programme was 86.3%. The study shows Hib immunization as an effective intervention while discussing continuing needs for Hib control in high risk populations. It also illustrates the benefit of immunization registers in the evaluation of immunization programmes and assessment of vaccine effectiveness.

A combined liquid Hib (PRP-OMPC), hepatitis B, diphtheria, tetanus and whole-cell pertussis vaccine: controlled studies of immunogenicity and reactogenicity.

We evaluated the immunogenicity and reactogenicity of a new liquid pentavalent combination vaccine, which incorporates a diphtheria, tetanus and whole-cell pertussis vaccine (DTP) with Hib (PRP-OMPC) and hepatitis B vaccine (HB), in a series of three studies involving 2156 infants. The vaccination schedule was 2, 4, 6 and 18 months for all studies. In addition, subjects in the third study also received a dose of monovalent hepatitis B vaccine at birth. The principal study was a randomised double blind trial of two separate, but concurrently administered vaccines in each of three groups: pentavalent vaccine [DTP-Hib-HB] plus placebo (Group A, n=619); quadrivalent vaccine [DTP-HB] plus Hib vaccine (Group B, n=620); and bivalent vaccine [Hib-HB] plus DTP (Group C, n=226). The second study (Group D, n=231) was an open trial of three separate, but concurrently administered licensed control vaccines (DTP, Hib and HB). The third study (Group E, n=460) administered a dose of monovalent hepatitis B vaccine at birth followed by pentavalent vaccine as for Group A. Subjects were bled prior to the 2- and 18-month vaccinations, and a month after the 6- and 18-month vaccinations. A diary card was used to record subject temperatures and other systemic and local clinical signs for 7 days after each vaccination. The pentavalent vaccine, whether or not preceded by a birth dose of hepatitis B vaccine, was generally well tolerated at all administration times, and had a reactogenicity profile similar to that observed for licensed vaccine controls. Diphtheria and tetanus antibody levels were substantially above protective levels in all study groups. The anti-HBs responses (% > or = 10 mIU/ml) following the 6-month dose of vaccines were, respectively, for Groups A-E: 83.2, 91.7, 96.5, 98.8 and 93.9%, and following the 18-month doses: 87.9, 97.5, 98.8, 98.8 and 92.8%. Anti-PRP responses (% > or = 1.0 microg/ml) following the 6-month dose for Groups A-D were 86.0, 90.5, 91.2, and 74.4%, and after the 18-month dose for Groups A-E were 97.3, 98.3, 98.1, 97.0, and 99.5%. Consistently higher geometric mean titres (GMTs) for pertussis antibodies to agglutinogens (Agg2, Agg3) and pertactin were recorded for the pentavalent vaccine compared to the licensed control vaccine, though they were somewhat lower for pertussigen (PT). Except for the hepatitis B response, antibody responses induced by the pentavalent vaccine to all antigens with a schedule commencing at 2 months of age and completed at 18 months were equivalent to responses to the same antigens induced by the separate, but concurrently administered licensed control vaccines. A regimen of a birth dose of hepatitis B vaccine followed by pentavalent vaccine at 2, 4, 6 and 18 months was not countered by any clinically significant decrease in seroresponses.

Experimental human gonococcal urethritis: 250 Neisseria gonorrhoeae MS11mkC are infective.

Neisseria gonorrhoeae MS11mkA (mkA) expresses one 3.6-kDa lipooligosaccharide (LOS). Variant MS11mkC (mkC), expressing four larger LOSs, occurs in vitro among mkA at a frequency of 10(-3). Infectivity of these variants was compared in 2 groups of volunteers inoculated with approximately 40,000 piliated, Opa- gonococci of either strain. The mkC variant infected 5 of 5 while mkA infected only 2 (40%) of 5. Gonococci recovered from the mkA infections showed a transition toward the mkC LOS phenotype. The mkA inoculum contained approximately 40 mkC gonococci. These data confirmed earlier studies and suggested that small numbers of mkC gonococci would be infective. This hypothesis was tested in three more experiments. In two, volunteers were inoculated with 250 or 1250 mkC, infecting 3 of 7 in each group, and in the third, 1600 mkC infected 2 of 6, resulting in a total of 8 of 20 infected by < or = 1600 mkC. Gonococci shed by infected volunteers maintained the mkC LOS phenotype but shifted from Opa- to Opa+. Thus, LOS and opacity protein, as well as pilus, are gonococcal virulence factors.

Inflammatory cytokines produced in response to experimental human gonorrhea.

Inflammatory cytokine production in men was examined after intraurethral challenge of volunteers with Neisseria gonorrhoeae MS11mkA or MS11mkC. Increased interleukin (IL)-8, IL-6, and tumor necrosis factor-alpha (TNF-alpha) were detected in urine before the onset of symptoms and peaked simultaneously with the detection of IL-1 beta at the onset of symptoms. Urine cytokine levels returned to baseline or near baseline within 48 h after antibiotic therapy. In plasma, IL-8, TNF-alpha, IL-1 beta, and IL-6 were elevated at the onset of symptoms in 9, 5, 4, and 3 of 10 subjects, respectively, and returned to near normal within 48 h after treatment. IL-1 alpha and granulocyte-macrophage colony-stimulating factor were not consistently detected in urine or plasma after challenge. Cytokine mRNA transcripts in peripheral blood mononuclear cells were not altered by the infection. The findings suggest that IL-8, IL-6, and possibly TNF-alpha were produced at the local site of infection, whereas IL-1 beta was derived from infiltrating leukocytes.

Efficacy, safety, and immunogenicity of a meningococcal group B (15:P1.3) outer membrane protein vaccine in Iquique, Chile. Chilean National Committee for Meningococcal Disease.

A meningococcal group B (15:P1.3) outer membrane protein vaccine was tested for efficacy in a randomized, double-blind controlled study in Iquique, Chile. A total of 40 811 volunteers, ages 1-21 years, enrolled in the study. Volunteers received two doses of vaccine six weeks apart by jet injector. Both the experimental vaccine and the control vaccine (Menomune, A, C, Y and W135 meningococcal polysaccharide vaccine) were well tolerated with minor side-effects. Active surveillance for suspected cases of meningococcal disease was conducted for 20 months in Iquique. Eighteen cases of group B meningococcal disease were confirmed during the 20 months. Efficacy was estimated to be 51% (p = 0.11) for all ages combined. In children aged 1-4 no protection was evident, but in volunteers aged 5-21 vaccine efficacy was 70% (p = 0.045). The IgG antibody response by ELISA was characterized by a large booster effect after the second dose, followed by a substantial drop in antibody levels by 6 months. The youngest children had the highest responses. The bactericidal antibody response, on the other hand, was characterized by the lack of a significant booster response, higher responses in the older children, and an increase in the geometric mean titer in the later months of the study in the older children.

Public health implications of emerging vaccine technologies.

The field of public health and medicine stands to benefit immensely from the emerging vaccine technologies and improved application of existing technologies. Technological advances may promote: (1) greater flexibility and simplicity in the design and operation of immunization campaigns or ongoing prevention programs, including reduction in number of vaccine doses, cold chain elimination, slow-release/prolonged antigenic stimulation, reduced cost and hazard and increased ease of administration through noninvasive, oral delivery systems, greater population levels of immunization and health; (2) the development of documents by FDA, WHO, and other regulatory authorities and groups, to assist the manufacturer in the appropriate manufacturing, preclinical, and clinical development of these new vaccines; (3) a greater array of vaccines to protect the civilian and military populations; (4) increased vaccine potency; (5) vaccines eliciting mucosal immunity, cytotoxic T cells, and/or neutralizing antibody. At the end of the 20th century there remain many unconquered pathogens and noninfectious indications for which medical science suggests that vaccines could be effective. New technologies may provide the best hope to address this wide array of public health needs.

Safety, immunogenicity and limited efficacy study of a recombinant Plasmodium falciparum circumsporozoite vaccine in Thai soldiers.

Thai soldiers were vaccinated with a recombinant protein derived from the central repeat region of the circumsporozoite (CS) protein of Plasmodium falciparum conjugated to Toxin A (detoxified) of Pseudomonas aeruginosa (R32Tox-A) to evaluate its safety, immunogenicity and efficacy. In a randomized, double-blind manner, 199 volunteers received either R32Tox-A or a control vaccine at 0, 8 and 16 weeks. Immunization was performed in a malaria non-transmission area, after completion of which volunteers were deployed to an endemic border area and monitored closely to allow early detection and treatment of infection. The vaccine was found to be safe and to elicit antibody responses in all vaccinees. Peak CS antibody (IgG) concentrations in malaria-experienced vaccinees exceeded those in malaria-naive vaccinees (mean 40.6 versus 16.1 micrograms ml-1; p = 0.005) as well as those induced by previous CS protein-derived vaccines and observed in association with natural infections. A log-rank comparison of time to falciparum malaria revealed no differences between vaccinated and non-vaccinated subjects. Secondary analyses revealed that CS antibody levels were lower in vaccinee malaria cases than in non-cases, 3 and 5 months after the third dose of vaccine (p = 0.06 and p = 0.014, respectively). Because antibody levels had fallen substantially before peak malaria transmission occurred, the question of whether high levels of CS antibody are protective remains to be resolved.

Serologic response to Helicobacter pylori among children and teenagers in northern Chile.

The serologic response to Helicobacter pylori was determined in 388 children and teenagers living in Iquique, Chile by using an IgG enzyme-linked immunosorbent assay. Serum antibody levels, as measured by optical density, correlated strongly with age. Increases in the mean antibody level were seen primarily after age five, with rates of seropositivity increasing to > or = 70% among teenagers. The reasons for this age-related pattern of acquisition of infection remain to be determined.

Antibiotic susceptibility survey of Neisseria gonorrhoeae in Thailand.

The antibiotic susceptibilities of Neisseria gonorrhoeae isolates obtained from patients attending sexually transmitted disease clinics in Cholburi and Bangkok, Thailand, were determined by agar dilution. Some 28.2% of isolates produced beta-lactamase. A total of 97.9% of beta-lactamase-positive and 51% of beta-lactamase-negative isolates tested were resistant to penicillin (MICs, greater than or equal to 2 micrograms/ml), 70% of isolates tested were resistant to tetracycline (MICs, greater than or equal to 2 micrograms/ml), and 91% of isolates tested were susceptible to spectinomycin (MICs, less than or equal to 64 micrograms/ml). The MICs for 90% of isolates for the other drugs tested were 2 micrograms/ml for erythromycin, 2 micrograms/ml for cefoxitin, 1 micrograms/ml for cefuroxime, 0.125 micrograms/ml for cefpodoxime, 0.06 micrograms/ml for cefotaxime, 0.25 micrograms/ml for ceftazidime, 0.03 micrograms/ml for ceftizoxime, 0.03 micrograms/ml for ceftriaxone, 0.03 micrograms/ml for cefixime, 0.06 micrograms/ml for aztreonam, 0.008 micrograms/ml for ciprofloxacin, 0.125 micrograms/ml for norfloxacin, and 0.075 micrograms/ml for ofloxacin. Fewer than 1.5% of isolates were resistant to the extended-spectrum cephalosporins tested. Some 0.3% or fewer isolates were resistant to broad-spectrum cephalosporins, fluoroquinolones, or the monobactam aztreonam. Antibiotic resistance among N. gonorrhoeae isolates from Cholburi and Bangkok in May 1990 appeared to be primarily limited to penicillin and tetracycline, which are no longer used to control gonorrhea. Spectinomycin, which has been in general use against gonorrhea in Thailand since 1983, has dwindling utility, with resistance at a level of 8.9%.

Age-specific prevalence of serum antibodies to the invasion plasmid and lipopolysaccharide antigens of Shigella species in Chilean and North American populations.

Shigella species have virulence plasmids that encode outer membrane proteins (invasion plasmid antigens, Ipa) associated with pathogenicity. Western blots were used to detect antibodies to Ipa in sera from 390 Chilean children, and these responses were compared with those of a US population of infants and adults. Antibodies to lipopolysaccharide (LPS) of Plesiomonas shigelloides and Shigella flexneri 2a were measured by ELISA. Among the Chileans, there was an age-related acquisition of Ipa antibodies, with 28% of 1-year-olds and 100% of children greater than or equal to 10 years showing positive responses. In contrast, none of the US infants and only 38% of the adults had antibodies to Ipa. Levels of LPS antibodies were also found to increase in an age-related manner among the Chileans. These results corroborate findings of previous epidemiologic studies which show that Shigella infections are endemic in Chile, as in other developing countries. The measurement of Ipa and LPS antibodies is a useful seroepidemiologic tool for investigating previous exposure to Shigella species in populations.

Expression of paragloboside-like lipooligosaccharides may be a necessary component of gonococcal pathogenesis in men.

To learn how lipooligosaccharide (LOS) phase variations affect pathogenesis, we studied two male volunteers who were challenged intraurethrally with Neisseria gonorrhoeae that make a single LOS of 3,600 daltons and sequentially followed LOS expression by gonococci as urethritis developed. LOS variation occurred in vivo. Signs and symptoms of gonorrhea began with the appearance of variants making 4,700-dalton LOS that are immunochemically similar to glycosphingolipids of human hematopoietic cells (Mandrell, R.E., J.M. Griffiss, and B.A. Macher. 1989. J. Exp. Med. 168:107) and that have acceptors for sialic acid. A variant that appeared at the onset of leukorrhoea was shed by 34/36 men with naturally acquired gonorrhea at the time they sought medical attention; the other two shed the variant associated with dysuria. None shed the challenge variant. These data show that in vivo phase shifts to higher molecular mass LOS that mimic human cell membrane glycolipids are associated with the development of gonococcal leukorrhea.

Efficacy trial of a parenteral gonococcal pilus vaccine in men.

A randomized, placebo-controlled, double-blind efficacy trial of a purified gonococcal pilus vaccine composed of a single pilus type was tested in 3123 men and 127 women volunteers. Either 100 micrograms of vaccine or a placebo was given intradermally on day 1 and day 14. Each group was evenly matched with respect to age, sex, prior history of a sexually transmitted disease, sexual exposure during the study and attrition from the study. None of the women volunteers acquired gonorrhoea during the trial. In the male volunteers, 108 vaccine and 102 placebo recipients acquired gonorrhoea 15 days or later after the initial immunization. Vaccines developed a sustained ELISA antibody response to homologous and heterologous pili, but the latter titres were approximately 40% as high as the homologous pilus antibody rises. There were, however, no increases in inhibition of attachment antibody (IEA) titres. Local antibodies (semen) against homologous and heterologous strains were also elicited (ELISA). The vaccine was safe and did not alter the clinical expression of disease. This gonococcal pilus vaccine composed of a single pilus type failed to protect men against gonococcal urethritis.

Human immunization with Pgh 3-2 gonococcal pilus results in cross-reactive antibody to the cyanogen bromide fragment-2 of pilin.

In 1983, a gonococcal pilus vaccine failed to show protection in a large, placebo-controlled, double-blind field trial. The epitopic response to this vaccine was investigated in a random subgroup of 20 vaccine recipients. Using Western blot analysis of the immunizing pilus and its cyanogen bromide (CNBr) fragments, IgG antibody to pilin was detected before immunization in all individuals. Preexistent antibody to the CNBr-2 and CNBr-3 fragments of pilin was detected in 65% and 5% of individuals, respectively. Pilus immunization resulted in a vigorous response to the CNBr-2 fragment in 100% of the individuals tested; only 33% developed antibody to the CNBr-3 fragment. Absorptions of postimmunization sera with different gonococcal strains resulted in either complete or partial removal of antibody to the CNBr-2 fragment. In the context of an unsuccessful vaccine trial, these results suggest that antibody to the CNBr-2 fragment of pilin may not be protective.

Expression of outer membrane protein II by gonococci in experimental gonorrhea.

Gonorrheal urethritis was induced in three males by intraurethral instillation of predominantly pilus+ protein II- gonococci. Virtually all gonococci reisolated from the infected men exhibited protein II+ phenotype. The reisolated gonococci expressed five distinct outer membrane protein II species. Protein IIc+ organisms predominated in urines of all three subjects, but variants expressing this particular protein II were rarely spawned in vitro by input organisms. Protein IIc+ gonococci appeared early in one man's infection; they were joined later by variants that displayed eight other protein II phenotypes, including protein II-. These results show that input protein II- gonococci are supplanted by protein IIc+ variants during incipient gonorrheal urethritis. As infection progresses, a broader variety of protein II+ variants appears.

A prospective randomized trial of ofloxacin vs. doxycycline in the treatment of uncomplicated male urethritis.

One hundred fourteen men with uncomplicated urethritis were randomized to receive 1 week of therapy with either doxycycline (100 mg twice daily) or ofloxacin (300 mg twice daily). Of the 109 men completing the post-treatment visit, 56 received ofloxacin and 52 (93%) were clinically cured. Forty four (83%) of the 53 men treated with doxycycline were cured. All 30 patients with gonorrhea (including three with penicillinase-producing Neisseria gonorrhoeae [PPNG] isolates) who were treated with ofloxacin became culture-negative, as compared with 32 of 34 patients receiving doxycycline. In contrast, three of 18 patients with Chlamydia trachomatis were microbiologic failures after ofloxacin therapy, while all ten treated with doxycycline were cured. Adverse effects of both treatment regimens were generally mild, and compliance was excellent except for one patient receiving doxycycline. These results show that ofloxacin, in a dosage of 300 mg taken orally twice daily for seven days, is an effective treatment for uncomplicated urethritis in men but may not reliably cure chlamydial infections.

Spectinomycin disk zone diameter as a predictor of outcome in clinical treatment of gonorrhea.

The MICs for 41 Neisseria gonorrhoeae strains from patients receiving spectinomycin treatment were determined by the agar dilution method and compared with the zones of inhibition produced by disks containing 100 micrograms of spectinomycin. Our data demonstrated a good correlation between the two methods. Moreover, a zone of inhibition of less than or equal to 15 mm was a good predictor of clinical treatment failures with spectinomycin.