The utility of seroepidemiology for tracking trends in pertussis infection.

Comparing pertussis epidemiology over time and between countries is confounded by differences in diagnostic and notification practices. Standardized serological methods applied to population-based samples enhance comparability. Population prevalence of different levels of pertussis toxin IgG (PT IgG) antibody, measured by standardized methods, were compared by age group and region of Australia between 1997/1998 and 2002. The proportion of 5- to 9-year-olds with presumptive recent pertussis infection (based on IgG levels >or=62.5 ELISA units/ml) significantly decreased in 2002, consistent with notification data for the same period and improved uptake of booster vaccines following the schedule change from whole-cell to acellular vaccine. In contrast, recent presumptive infection significantly increased in adults aged 35-49 years. Population-based serosurveillance using standardized PT IgG antibody assays has the potential to aid interpretation of trends in pertussis incidence in relation to vaccine programmes and between countries.

Chronic biological false-positive reactions to serological tests for syphilis in blood donors.

Problem sera from 375 blood donors were investigated for biological false-positive reactions to serological tests for syphilis. Problem sera are those sera in which submitting laboratories have found a reactive result to a screening test for syphilis. On each serum a cardiolipin Wassermann reaction, a Venereal Disease Research Laboratory test, a Reiter protein-complement fixation test, a Treponema pallidum immobilization test, and a fluorescent treponemal antibody absorption test were performed. Of the sera 49.9% were found to be non-reactive in all five tests, 28.8% gave results indicating a diagnosis of syphilis, and 21.3% showed biological false-positive reactions. There were 80 sera from blood donors which gave biological false-positive reactions. A further specimen of serum from 67 of these donors was tested after an interval of a minimum of six months. Sixty-six of the sera showed chronic biological false-positive reactions. Some donors were only found reactive for the first time after they had given very many donations of blood. It is concluded that sudden blood loss, as in blood donation, appears to stimulate the production of excess reagin in certain individuals, causing a chronic biological false positive reaction to serological tests for syphilis. This may only appear after several blood donations have been made.

The rapid plasma reagin (circle) card test in biological false positive and leprosy sera.

The rapid plasma reagin (RPR) circle card and the Venereal Disease Reference Laboratory (VDRL) slide test results were compared on a group of sera known to show biological false positive (BFP) reactions to reagin detection tests for syphilis. The RPR test was more specific than the VDRL test on the sera selected, ie, it gave fewer false positive results than the VDRL test. However, in a group of presumed normal sera, the RPR test gave BFP reactions while the VDRL test gave none. The RPR test gave fewer BFP reactions than the VDRL test in 269 sera from patients with lepromatous leprosy.

The Treponema pallidum haemagglutination (TPHA) test in biological false positive and leprosy sera.

The Treponema pallidum haemagglutination (TPHA) test was carried out on 274 sera known to show biological false positive reactions to reagin tests for syphilis. The Treponema pallidum immunization (TPI) and fluorescent treponemal antibody absorption (FTA-ABS) tests were non-reactive on all these sera. Thirty-one or 11.3% showed reactive results in the TPHA test. Sera from 267 people who had lepromatous leprosy were also tested in the TPHA test. Fourteen sera were reactive in the TPHA, TPI, and FTA-ABS tests and were from people who had both syphilis and leprosy. Biological false positive reactions were shown by 26 of the leprosy sera, of which three or 11.5% were also reactive in the TPHA test. A further four sera in the leprosy group were reactive only in the TPHA test. The possible cause of false reactive TPHA test results is discussed. It was concluded that where reagin and TPHA tests are reactive in a person who has no history or clinical signs of syphilis, the serum should be referred for TPI and FTA-ABS testing.

Failure of penicillin treatment of yaws on Karkar Island, Papua New Guinea.

The endemic treponematosis yaws remains a significant cause of morbidity in many tropical countries, despite mass treatment campaigns to eradicate it. An outbreak of yaws in Marup village on Karkar Island, Papua New Guinea in 1988 provided an opportunity to monitor the outcome of treatment with penicillin over an extended period. Thirty-nine children with clinical yaws (6% of 632 examined) were monitored clinically and serologically, for nearly two years after mass treatment of all villagers with the World Health Organization recommended dosages of benzathine penicillin. Lesions resolved within one month of treatment in all but four (10%) children, three of whom were initially successfully retreated. Before treatment, the Venereal Disease Research Laboratory (VDRL) test result was reactive in 67% of the children and treponema-specific IgM antibody test results were reactive in 41%. Within six months of treatment, of those reactive, the VDRL titer decreased significantly in 25 (96%) of 26 and IgM antibody test results became negative in 13 (81%) of 16 children. However, by the end of follow-up, 11 (28%) of the 39 children had developed clinical and/or serologic evidence of relapse. In these children, response to further treatment was slow and, in three, evidence of active infection persisted or recurred, despite repeated courses. Exogenous reinfection was unlikely in this isolated community, in which the occurrence of yaws was closely monitored after universal treatment. Treatment failure was most likely to have been due to reduced susceptibility to penicillin of Treponema pallidum subsp. pertenue.

Treponema pallidum western blot: comparison with the FTA-ABS test as a confirmatory test for syphilis.

We developed a Treponema pallidum Western blot and compared the results with Treponema pallidum particle agglutination (TPPA) and fluorescent treponemal antibody absorption (FTA-ABS) tests. The Western blot was deemed reactive if the serum reacted with at least three major antigenic bands (TpN47, TpN44.5, TpN17, TpN15). The sensitivities of the Western blot, TPPA and FTA-ABS, were all 100% and the specificities of the Western blot, TPPA and FTA-ABS were 100%, 100% and 94.5% respectively. In 52 problem sera, reactive in only one treponemal test, the agreement between the Western blot and TPPA (61.5%) was significantly better than between Western blot and FTA-ABS (38.5%). The individual sensitivities and specificities of TpN47, TpN44.5, TpN17, TpN15 were 100%, 100%, 96%, 100% and 20%, 96%, 100%, 100% respectively. We conclude that the Western blot is a useful additional confirmatory test or alternative to the FTA-ABS and that a more sensitive and specific criterion for the Western blot would be reactivity with TpN15 and two of the three other major antigens.

A survey of sexually transmitted diseases in five STD clinics in Papua New Guinea.

The first multicentre survey of sexually transmitted diseases (STDs) performed in Papua New Guinea was conducted in STD clinics in five towns, Port Moresby, Goroka, Rabaul, Lae and Daru, from September 1989 to May 1990. Infections with Neisseria gonorrhoeae and Chlamydia trachomatis (alone or in combination) were common. Penicillinase-producing N. gonorrhoeae (PPNG) represented 44% of all gonococcal isolates but significant intrinsic resistance to penicillin was not found. Of the other antibiotics tested, significant elevation of minimum inhibitory concentration (MIC) was common only for tetracycline, although no high-level tetracycline resistance was detected. C. trachomatis was detected by direct immunofluorescence (DIF) in 26% of 210 males and 27% of 64 females. 10% (21/210) of males and 11% (7/64) of females were both DIF positive for C. trachomatis and culture positive for N. gonorrhoeae. Of 203 males and 78 females tested, 5% and 12%, respectively, had serological evidence of current syphilis infection. Clinically, genital ulcer disease was most commonly due to syphilis, donovanosis or genital herpes, while specific vaginal infections were commonly seen in female patients attending Port Moresby and Lae STD clinics.

Population-based seroprevalence of Neisseria meningitidis serogroup C capsular antibody before the introduction of conjugate vaccine, in Australia.

Neisseria meningitidis serogroup C (NMC) conjugate vaccine was introduced, in Australia, in 2003. Our aims were to determine pre-immunisation IgG NMC seroprevalence and evaluate an enzyme-linked immunosorbent assay (ELISA), previously validated against the serum bactericidal assay (SBA). 2409 sera, collected in 2002, from subjects aged 2-34 years, were tested. The geometric mean concentration (GMC) of NMC anticapsular IgG was 0.38 U/mL in subjects under 19 years and it increased to 0.67 U/mL for those aged 30-34 years. Variation in GMC correlated with reported NMC disease incidence and was higher in males than females (0.52 U/mL versus 0.41 U/mL; p=0.005). The ELISA appears suitable for serosurveillance but the IgG level that correlates with protection needs further investigation. Serosurveys will be repeated to monitor the impact of vaccination.

National serosurvey of cytomegalovirus in Australia.

In anticipation of the development of a vaccine against cytomegalovirus (CMV), we conducted a large, nationally representative serosurvey to examine the seroprevalence of CMV in Australia. Sera were collected opportunistically from laboratories around Australia. Age- and gender-representative samples were tested for CMV antibody. The population-weighted rate of CMV seropositivity in subjects between 1 and 59 years of age was 57% (95% confidence interval, 55.2 to 58.6%). An association between CMV seroprevalence and increasing age was recognized; however, little overall difference in seroprevalence between the sexes was found. The finding that high levels of CMV exposure occur in the first few years of life suggests that for a universal vaccination program to have maximal impact, the vaccine would need to be delivered to infants and have a long duration of protective efficacy. This is the first national serosurvey looking at cytomegalovirus in the Australian community. This study provides valuable information that can be used to examine the incidence of infection in the community and help focus the administration of a future CMV vaccine to appropriate target populations.

Evaluation of two enzyme immunoassays for detection of immunoglobulin G antibodies to mumps virus.

To determine suitability for national serosurveys, we compared two commercial enzyme-linked immunosorbent assays (ELISAs) for mumps antibody, Enzygnost Anti-Parotitis-Virus/IgG (which uses a whole-virus antigen) and Microimmune Mumps IgG Screen ELISA (which uses a recombinant nucleoprotein antigen), by testing 1,915 opportunistically collected sera submitted to diagnostic laboratories across Australia in 1997 to 1998. The proportion of positive results increased with age in both ELISAs but was significantly higher with the Microimmune than with the Enzygnost ELISA overall (88% versus 63%; P < 0.01) and in all age groups. However, the proportion of equivocal results was significantly higher with the Enzygnost than with the Microimmune ELISA (9% versus 4%; P < 0.01). Of the 572 sera with discrepant or equivocal results, 508 had sufficient sample remaining to perform the neutralization test (NT). A proportion with concordant results in both ELISAs were also tested by the NT. For sera with discrepant results, there was significantly better agreement between the NT and Microimmune than between the NT and Enzygnost (310/444 [70%] versus 135/348 [39%]; P < 0.01). Of 64 sera with equivocal Microimmune results, 45 (70%) were positive in the NT compared with 140 of 160 (88%) equivocal Enzygnost results (P < 0.01). Compared with the NT, the Microimmune ELISA is more sensitive (96% versus 80%) but apparently less specific (36% versus 85%) than the Enzygnost ELISA. However, this is likely to be due to the generally lower sensitivity of the NT, since the Microimmune results reflect expected seroprevalence, based on vaccine uptake in the age groups studied. We conclude that the Microimmune ELISA is a more appropriate assay than the Enzygnost ELISA for estimation of mumps seroprevalence.

Evaluation of immunoglobulin G enzyme immunoassay for serodiagnosis of yaws.

A commercially available enzyme immunoassay (EIA), the Captia Syphilis-G immunoglobulin G (IgG) EIA, for the detection of IgG antibodies to Treponema pallidum was evaluated for use as a screening test for yaws (Treponema pallidum subsp. pertenue). The IgG EIA was compared with the fluorescent treponemal antibody absorption (FTA-ABS) test. All sera were also examined by the T. pallidum hemagglutination test and the Venereal Disease Research Laboratory test. Serum samples from 271 subjects (23 control serum samples from an area nonendemic for yaws, 58 control serum samples from an area endemic for yaws, and 190 serum samples from yaws patients and contacts) were investigated. The overall agreement between the IgG EIA and the FTA-ABS test was 90%, the sensitivity was 99%, and the specificity was 70.2%. The specificity fell as the endemicity of the disease increased: from 94.4% in the nonendemic area controls to 86.4% in the endemic area controls and to 52.3% in the yaws contacts. There was no difference in specificity between children and adults within each of the three groups. Fifteen children with clinical yaws were monitored for 9 months after treatment. The level of treponemal antibody fell consistently in 9 of the 15 children as measured by the antibody index (ratio of absorbance of the test serum to the mean absorbance of the low-titer-positive controls). Reinfection was seen in three children, with the antibody index rising with the Venereal Disease Research Laboratory test titer. The Captia Syphilis-G test is a sensitive assay for the detection of treponemal antibodies in yaws patients. However, the apparent low specificity of the test in the yaws endemic area limits its use as a screening test for yaws.

Treponemal infection in the Australian Northern Territory aborigines.

For many years, a moderate to high prevalence of positive reactions to standard tests for syphilis (STS) has been found in sera from the aboriginal inhabitants of the Northern Territory of Australia. In the survey reported here, people living in 18 areas of the Northern Territory were sampled to determine if the positive STS results were due to treponemal infection and, if so, to what extent this was endemic syphilis, yaws, or venereal syphilis. The results of the Treponema pallidum immobilization test were taken to indicate the presence or absence of treponemal disease in the subject. Clinically, no cases of active treponemal infection were seen, though findings on old infections were difficult to interpret in the older age groups. The prevalence of treponemal infection varied from 3.4% to 58.0% in the areas tested. No serological evidence of treponemal infection in children under 15 years of age was found in 6 areas, while in 12 areas it varied from 2.2% to 32.6%. Sera from 60 people who had no clinical signs of treponemal infection gave high-titre CWR and VDRL test results. It was concluded that yaws, endemic syphilis, and probably venereal syphilis are to be found in the aboriginal population.

Modified indirect hemagglutination test for detection of treponemal antibodies in finger-prick blood.

A modified indirect hemagglutination test for the detection of treponemal antibodies was developed for use with finger-prick blood. By using paired serum and absorbed finger-prick blood from 58 patients from an area previously endemic for yaws and 12 patients without yaws, the modified hemagglutination test was compared with a hemagglutination test for Treponema pallidum and the fluorescent treponemal antibody absorption test. The modified hemagglutination test showed 100% specificity and an overall agreement of 96.5% with the hemagglutination test for T. pallidum and 94.8% with the fluorescent treponemal antibody test. The modified hemagglutination test appears to be a simple and economical test that is suitable for use in large epidemiological surveys for yaws.

Treponemal serology on Bali Island, Indonesia.

As part of a multidisciplinary study of the population of Bali, Indonesia, treponemal serology was carried out on 2452 serum samples from subjects of both sexes. Sera reactive to the Treponema pallidum immobilisation test (TPI) were found in 81 (3.3%) subjects with a male prevalence of 4% and a female prevalence of 2%. All the reactive sera were from villagers. Of 1118 students sampled in various towns, none had reactive TPI tests. The prevalence of reactive sera varied greatly from one village to another; up to 50% of the sera examined were reactive. Geographical and socioeconomic analyses of the data show a strict correlation between poor socioeconomic status and high reactivity rates to the TPI test. Fifty-seven per cent of all the reactive sera originated from subjects living in two districts where yaws had recently been reported. Only three of the 1406 subjects, aged 15-29 years, had reactive sera. The reactivity rate steadily increased in the age groups 30-44, 45-59, and 60 years and over. Biological false-positive reactions occurred in 3.8% of the sera tested.