Sexual behaviours determined incidence and reinfection, regardless of healthcare setting. Our results suggest annual screening of women aged 16-24 years who are chlamydia negative, or sooner if partner change occurs. Rescreening chlamydia-positive women within 6 months of baseline infection may be sensible, especially if partner change occurs or all partners are not treated.
SUMMARY Sera from 105 blood donors and eight patients with brucellosis were examined for anti-brucella IgG and IgM by a radioimmune technique. A pooled standard was used for comparison and evaluation. The upper limit of the 99% confidence interval on the mean of both immunoglobulin classes in blood donor sera was below 7 units/ml. Antibody response was shown in three acute, two relapsing, two chronic, and one asymptomatic cases. Values of up to 300 units/ml of both classes were found in the acute cases. Chronic sufferers showed lower concentrations of antibody. Relapsing cases showed increases comprising mainly IgG. The assay method, which shows general concordance with the results of conventional tests, is useful and measures individual immunoglobulin classes directly.Most human cases of brucellosis are diagnosed by recognising the symptoms and by demonstrating the antibodies in the serum. The organism may be isolated from the blood, but bacteraemia is intermittent.' Reliance is therefore placed on immunological procedures, which must be both accurate and informative.Conventionally, antibodies have been studied using the serum agglutination test, the complement fixation test, and the indirect antihuman globulin assisted agglutination test. From these results the presence and relative proportions of anti-brucella immunoglobulins (IgG and IgM) are inferred and thus the stage of the disease and its activity in the patient are estimated.24Previous workers have shown that the titres obtained in conventional serological tests are not absolutely related to the presence and relative pro-
Studies have suggested that positivity can be used to estimate the prevalence of Chlamydia trachomatis in large-scale chlamydia screening programmes. A recent pilot of opportunistic screening in England estimated that the prevalence among 16-24-year-old women in Portsmouth and Wirral was 9.8% and 11.2%, respectively. This study assessed the continued validity of positivity as an approximate for prevalence. We re-analysed data from the Chlamydia Screening Pilot to estimate positivity,calculated as total positive tests divided by total tests, and compared these estimates with the previously reported prevalence, measured as the number of women testing positive divided by the total number of women screened. Overall positivity was 9.4% in Portsmouth and 11.0% in the Wirral; these estimates were not statistically different from prevalence, regardless of health-care setting, age group or symptoms. We conclude that positivity can be used as a proxy for prevalence.
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