Pulmonary tuberculosis in Norwegian patients. The role of reactivation, re-infection and primary infection assessed by previous mass screening data and restriction fragment length polymorphism analysis.
SETTING: Norwegian patients with pulmonary tuberculosis notified to the National Tuberculosis Register in 1975, 1985 and 1995. OBJECTIVE: To assess the proportion of cases attributable to endogenous reactivation, exogenous re-infection and primary infection. DESIGN: We reviewed patients notified with sputum smear and/or culture confirmed pulmonary tuberculosis in 1975 (50% random sample, 95 cases), 1985 (133 cases) and 1995 (70 cases). Information on previous chest X-ray, tuberculin and BCG status was collected from mass screening data files. Strains from 54 patients in 1995 were analysed by IS6110 restriction fragment length polymorphism (RFLP) typing and compared with culture-positive patients notified between 1994 and 1997. RESULTS: Most patients had previously had tuberculosis (65% in 1975, 53% in 1985 and 61% in 1995), either notified with tuberculosis or with X-ray findings indicating previous tuberculosis. Another 10% had a prior infection, but normal X-rays. No previous tuberculosis infection or disease was found in 10% in 1975, 19% in 1985, and 16% in 1995. Of 54 patients with RFLP results, three were caused by laboratory contamination. Of the remaining 51, eight (16%) belonged to a cluster. Among 45 patients with results of both RFLP typing and mass screening, 37 (82.2%) were probably caused by reactivation, six (13.3%) by re-infection and two (4.4%) by primary infection. CONCLUSION: Pulmonary tuberculosis in Norwegian patients can mainly be attributed to reactivation, predominantly in persons with previous changes on chest X-ray.