Multisite pooling study using ligase chain reaction in screening for genital Chlamydia trachomatis infections.

BACKGROUND: Ligase chain reaction (LCR), a nucleic acid amplification assay, is a highly specific and sensitive test for detecting Chlamydia trachomatis in cervical and urethral swabs as well as first-void urine specimens. GOAL: To examine the suitability of using the LCR test to detect C trachomatis in pooled cervical specimens. STUDY DESIGN: The performance of LCR in pooled specimens was compared with individual specimen testing at six laboratories using 3,170 cervical swab specimens randomly selected from specimens received for routine testing in the participating laboratories. These samples then were combined consecutively into 634 pools of 5 specimens and 317 pools of 10 specimens. A reduced sample to cutoff ratio of 0.2 or more was used for the pooled specimens. RESULTS: Of the 188 positive specimens (98.9%), 186 were identified when single specimens were analyzed. When pools of 5 or 10 specimens were evaluated, 99.5% and 98.9% of the positive swabs, respectively, were identified correctly. Two positive specimens were detected only through pooling. CONCLUSIONS: Pooling samples for detection of C trachomatis by LCR is sensitive and specific. Depending on the prevalence of infection (positivity), LCR testing may result in cost savings, as compared with individual testing of specimens.

Performance characteristics of the Gen-Probe Probe Competition Assay used as a supplementary test for the Gen-Probe PACE 2 and 2C assays for detection of Chlamydia trachomatis.

The performance characteristics of the Gen-Probe Probe Competition Assay (PCA) used in conjunction with the Gen-Probe PACE 2 and 2C direct detection assays for Chlamydia trachomatis were examined. Data collected by five public health laboratories by using the Gen-Probe PACE 2 were pooled and analyzed. Of 25,081 endocervical and male urethral specimens tested by the PACE 2 assay, 773 were tested by PCA. Of 334 specimens initially positive by the PACE 2 assay with an initial PACE 2 result of greater than 2,000 relative light units (RLU), 333 (99.7%) were positive by PCA while 242 of 339 (71.4%) specimens with an initial result between the cutoff and 2,000 RLU were positive by PCA, and 35 of 100 (35%) specimens with initial results between 200 RLU and the cutoff were positive by PCA. An additional 10,938 specimens were tested by the PACE 2C assay. Of these, positive PCA results were obtained for 187 of 188 (99.5%) specimens with initial results of greater than 2,000 RLU, 99 of 163 (60.7%) of specimens in the range of cutoff to 2,000 RLU, and 12 of 100 (12%) in the range of 200 RLU to the cutoff. These results indicate that specimens greater than 2,000 RLU do not require a supplemental test and that additional positive results can be obtained by testing specimens with an initial result below the cutoff.

Factors associated with the geographic variation of reported Chlamydia infection in Minnesota.

BACKGROUND AND OBJECTIVES: In Minnesota, physicians have been required to report cases of Chlamydia trachomatis infection since 1985. The distribution of reported cases suggests that there is substantial geographic variation in the rate of chlamydia infection. GOAL OF THIS STUDY: We conducted chlamydia screening at selected sites and a survey of primary care physicians in counties with high and low rates of reported chlamydia infection. We hypothesized that chlamydia infections are uniformly distributed in nonmetropolitan areas, and the geographic differences in reported cases can be attributed to variable testing and reporting practices by physicians. STUDY DESIGN: The number of reported female chlamydia cases per 1,000 women was calculated for each rural Minnesota county in 1990. Fourteen counties with high and low rates of reporting were selected for further investigation. From September to December 1991, universal chlamydia screening was carried out at 11 clinics serving patients in these counties. A questionnaire was mailed to all primary care physicians in these counties. RESULTS: In 1990, the rate of reported chlamydia cases was 4.7/100,000 and 0.1/100,000 for women living in the high-reporting and low-reporting counties, respectively. Chlamydia infection was present in 5.5% and 9.7% of women screened at selected clinics in high- and low-reporting counties, respectively. Physicians in high- and low-reporting counties did not differ significantly in terms of age, gender, number of pelvic exams, or frequency of chlamydia testing. However, physicians in high-reporting counties were significantly more likely to test for chlamydia when evaluating mucopurulent cervicitis or salpingitis, and they were more likely to test a woman whose sex partner had urethritis. Physicians in high-reporting counties were also more likely to have reported a case of chlamydia.

Prevalence of rabies specific antibodies in the Mexican free-tailed bat (Tadarida brasiliensis mexicana) at Lava Cave, New Mexico.

Adult female and juvenile Mexican free-tailed bats (Tadarida brasiliensis mexicana) were collected bimonthly at Lava Cave, New Mexico from May through September. The purpose of this study was to examine the prevalence of active rabies infection as well as to determine individual immune status in these hosts. All bats were bled and examined for rabies antibody (total antibody versus IgM) utilizing a modified serum neutralization test. The brains were removed and examined by the fluorescent rabies antibody (FRA) test. No significant difference was observed in the number of adults with rabies neutralizing antibody (total) over the study period. Significant differences in rabies neutralizing antibody (total) were observed among the juveniles sampled during July and August. The number of adults with IgM specific antibody was low (15 of 750, 2%) and did not fluctuate significantly. However, the number of juveniles with IgM antibody did show increased levels in August and September. The number of adults positive by the FRA was low (4 of 750, less than 1%) and did not appear to fluctuate significantly over the study period. The number of juveniles positive by the FRA was three and one-half times higher than observed for the adults (14 of 600, 2%). These results indicate that the Mexican free-tailed bat appears to be exposed to rabies virus shortly after birth as evident by its immune status. The low prevalence (4 of 750, less than 1%) of active infection as determined by the FRA and mouse inoculation and the high prevalence (514 of 750, 69%) of IgG antibody in the adult females indicate that the Mexican free-tailed bat recovers from rabies virus infection.

Evidence for prenatal transfer of rabies virus in the Mexican free-tailed bat (Tadarida brasiliensis Mexicana).

Fetuses were collected from four Mexican free-tailed bats (Tadarida brasiliensis mexicana) and a fetal bat cell (FBC) line was established and tested for its ability to support the replication of the ERA vaccine strain of rabies virus. Cytopathic effects were detected in ERA virus-inoculated as well as uninoculated FBC's. Immunofluorescent antibody testing of uninoculated FBC's provided no evidence for the presence of rabies virus. However, mice inoculated intracranially with supernatant fluid from uninoculated FBC's died. Enzyme-linked immunosorbent assay and immunofluorescent antibody testing revealed rabies virus in the brains of these mice. Tests with a panel of monoclonal antibodies indicated that the isolate was the same as that isolated from Mexican free-tailed bats from the southwestern United States. We conclude that the fetuses from which the FBC line was derived had been infected in utero with rabies virus. We believe this may represent the first observation of prenatal transfer of rabies virus in naturally infected bats.

Evaluation of blood collected on filter paper for detection of antibodies to human immunodeficiency virus type 1.

This study was undertaken to evaluate the sensitivity and specificity of a commercial enzyme immunoassay in detecting antibody to human immunodeficiency virus type 1 using whole-blood specimens collected onto filter paper. Results obtained with specimens collected onto filter paper were comparable with those obtained with the corresponding serum or plasma specimens.

Acquired immunodeficiency syndrome in low-incidence areas. How safe is unsafe sex?

Serum specimens from the cohort of persons who attended sexually transmitted disease clinics in New Mexico during a two-month period were tested for human immunodeficiency virus (HIV) antibody. Twenty-seven (2.0%) of 1374 serum specimens had repeatedly low-positive reactions by enzyme-linked immunosorbent assay testing, and 22 (1.6%) had repeatedly high-positive reactions. All sera (sufficient for testing by Western blot) with low-positive reactions gave negative results, and all sera (sufficient for testing by Western blot) with high-positive reactions gave positive results. All persons whose serum had high-positive reactions were male. Most (86%) had been seen at the only urban sexually transmitted disease clinic in New Mexico, and most (72%) were openly gay or bisexual. Of all gay and bisexual men evaluated, 14% (16/112) had high-positive reactions. Rapid plasma reagin positivity was significantly associated with HIV enzyme-linked immunosorbent assay low (false) positivity. The relatively high rate of HIV seropositivity among gay men with other sexually transmitted diseases indicates that transmission of acquired immunodeficiency syndrome is continuing in this low-incidence area and documents the need for testing and counseling programs in sexually transmitted disease clinics.

Comparison of four serotests for the detection of Dirofilaria immitis infection in dogs.

Three hundred two dogs were tested with 4 serotests for heartworm antigen (AG) or antibody (AB) and with the Knott test. The 4 serotests evaluated were an enzyme-linked immunosorbent assay (ELISA) for adult heartworm-specific AB (AB-ELISA), a quantitative, indirect immunofluorescent assay (IFA) for adult heartworm-specific AB (AB-IFA), an IFA test for microfilaria (MF)-specific AB (MF-IFA), and an ELISA for adult heartworm AG (AG-ELISA). The presence of heartworms was ascertained in all dogs by necropsy examination. Of 302 dogs, 20 (6.6%) had heartworms in the heart at necropsy. Of infected dogs, 9 (45%) had occult infections. Test sensitivities were 75%, 95%, 70%, and 75% for the AB-ELISA, AB-IFA, MF-IFA, and AG-ELISA, respectively. Test specificities were 85% (AB-ELISA), 77% (AB-IFA), 87% (MF-IFA), and 99% (AG-ELISA). The best agreement between serotest results and necropsy findings was obtained with the AG-ELISA (97%). The 4 serotests detected 86% (AB-ELISA), 100% (AB-IFA), 67% (MF-IFA), and 78% (AG-ELISA) of the dogs with occult heartworm infection. A significant (P less than 0.05) association between intestinal parasitism and positive heartworm test results was found with only AB-IFA. Seemingly, the Knott test, or some other concentration method for detecting circulating MF should be the first heartworm test performed. If the examination for MF is negative, the dog has clinical signs, and radiographic findings are suggestive of occult heartworm infection, then a serotest for adult heartworm AG is recommended.

Incidence of hepatitis B in the penitentiary of New Mexico.

A study was conducted to determine the incidence of hepatitis B (HB) in a prison population. Forty-seven per cent of 455 male prisoners had evidence of past HB infection. HB seropositivity was most strongly correlated with: 1) a history of IV drug abuse; 2) age; 3) total time in any prison; and 4) race. During a one-year study period there were no clinical cases of HB in the prison and the seroconversion rate was 0.8 per cent among prisoners still incarcerated.

Comparison of enzyme-linked immunosorbent assay, hemagglutination inhibition, and passive latex agglutination for determination of rubella immune status.

Hemagglutination inhibition, enzyme-linked immunosorbent assay (ELISA), and passive latex agglutination were used to test 495 human serum samples for determination of rubella immunity. Overall agreements for immune status were as follows: hemagglutination inhibition versus ELISA, 94.7% (469 of 495); hemagglutination inhibition versus passive latex agglutination (1:10 dilution), 99.2% (491 of 495); and passive latex agglutination (1:10 dilution) versus ELISA, 94.7% (469 of 495). Both ELISA and passive latex agglutination are satisfactory for rubella immunity screening, with the reservation that the ELISA method examined yielded a large number of false-negative results.

Low prevalence of hepatitis B infections among residents of an institution for the mentally retarded in New Mexico.

Residential institutions for the mentally retarded are considered high-risk settings for hepatitis B (HB) infection. Accordingly, HB vaccine is recommended for susceptible clients and selected staff of such facilities. However, a serologic screening program among 364 residents of Los Lunas Hospital and Training School (LLHTS) in New Mexico found only 11 residents to be anti-HBc positive (3%) and only one of these residents was also HBsAg-positive (0.3%). The unexpectedly low prevalence of HB infections at LLHTS probably reflects infrequent HB introductions into the institution. Using these serologic data, a vaccination program was instituted to prevent HB infection among LLHTS residents, thereby eliminating the need for mass screening and HB vaccination of LLHTS employees. Serologic screening among residents of other smaller institutions for the mentally retarded is recommended before design of HB prevention programs for clients and staff.

Problems in determining immune status in borderline specimens in an enzyme immunoassay for rubella immunoglobulin G antibody.

A total of 374 sera, found by enzyme-linked immunosorbent assay (Rubazyme; Abbott Laboratories, North Chicago, Ill.) to have borderline rubella antibody levels, were tested by hemagglutination inhibition. All sera had Rubazyme indexes in the range of 0.500 to 1.499. Rubazyme sensitivity was 59.0%, and specificity was 80.8%. The predictive value of Rubazyme-positive result was 91.4%, and that for a negative result was 36.4%. Immune and nonimmune results were significantly different between the two methods (P less than 0.001). The same sera were retested with the Rubazyme test, with an inter-run agreement of 75.3%. A significant difference in Rubazyme indexes between runs (P less than 0.001) was observed. An alternative method of testing specimens in the range close to the Rubazyme index cutoff value of 1.000 may be indicated.

An outbreak of influenza B in an elderly population.

An outbreak of influenza B occurred in an elderly population residing in a Minnesota nursing home between April 24 and May 21, 1979 and involved 129 (35.9%) of the 359 residents. Throat swabs from 11 and 19 acutely ill residents yielded influenza B virus similar to the B/Singapore/79 strain. Fourfold or greater increases in titer of complement-fixing or hemagglutination-inhibiting antibodies were detected in paired sera from 18 of the 19 persons affected and from three of 16 unaffected residents. Three hundred thirty-three (93%) of the 359 residents had received trivalent influenza virus vaccine in November 1978. The attack rate was age-specific and increased with age (z = 2.69; P = 0.007). Increasing susceptibility to influenza B with age in the elderly has not been previously demonstrated in this infrequently studied population. Increased risk for becoming ill was also found to be statistically associated with decreasing levels of care required and residence in closed wards and temporally associated with taking meals in the facility's dining areas.