Use of laboratory testing for genital chlamydial infection in Norway.

Abstract

OBJECTIVE--To assess the use of laboratory tests for genital chlamydial infection in Norway. DESIGN--Questionnaire survey of general practitioners' practice in chlamydial testing, retrospective survey of laboratory records, 1986-91, and prospective study of testing in one laboratory during four weeks. SETTING--All 18 microbiological laboratories in Norway (4.2 million population), including one serving all doctors in Vestfold county (0.2 million population). SUBJECTS--302 general practitioners. MAIN MEASURES--GPs' routine practice, methods used for testing, 1986-91, and sex specific and age group specific testing in 1991. RESULTS--201(69%) GPs replied to the questionnaire: 101(51%) would test all women younger than 25 years at routine pelvic examination, 107(54%) all girls at first pelvic examination, 131(66%) all pregnant women, and 106(54%) all men whose female partner had urogenital complaints. Nationwide in 1986, 122,000 tests were performed (2.9 per 100 population); 10% were positive and 51% were cell culture tests. In 1991, 341,000 tests were performed (8.0 per 100 population); 4.5% were positive and 15% were cell culture tests. 13,184 tests were performed in Vestfold in 1991 (6.6 per 100 population). The age group specific rates (per 100 population) among women were: age 15-19 years, 22.0(95% confidence interval 18.2 to 25.8); 20-24 years, 47.2(42.1 to 52.3); 25-29 years, 42.3(37.1 to 47.5); 30-34 years, 29.8(25.4 to 34.2); and 35-39 years, 12.5(9.5 to 15.5). CONCLUSIONS--GPs use liberal indications for testing. The dramatic increase in testing, especially by enzyme immunoassays, in populations with a low prevalence of infection results in low cost effectiveness and low predictive value of positive tests, which in women over 29 years is estimated as 17-36%. IMPLICATIONS--Doctors should be educated about the limitations of enzyme immunoassays in screening low prevalence populations, and laboratories should apply a confirmatory test to specimens testing positive with such assays.