Low tuberculosis notification in mountainous Vietnam is not due to low case detection: a cross-sectional survey

Abstract

Abstract Background Studies show that tuberculosis notification declines with increasing altitude. This can be due to declining incidence or declining case detection. In Vietnam notification rates of new smear-positive tuberculosis in the central mountainous provinces (26/100,000 population) are considerably lower than in Vietnam in general (69/100,000 population). In order to clarify whether this is explained by low incidence or low case detection, we aimed to assess the prevalence of new smear-positive tuberculosis among adults with prolonged cough in three mountainous provinces in central Vietnam. Methods A house-to-house survey of persons (≥ 15 years) was carried out in twelve randomly selected districts in 2003. Three sputum specimens were microscopically examined of persons reporting a prolonged cough (≥ 3 weeks). Case detection was assessed by the ratio between notification and prevalence. Results Of 68,946 included persons (95% response), 1,298 (1.9% 95%CI 1.8–2.2) reported a prolonged cough. Of these, eighteen were sputum smear-positive of whom two had had anti-tuberculosis treatment. The prevalence of new smear-positive tuberculosis was 27/100,000 (95%CI 11–44/100,000) and the notification rate was 44/100,000 among persons ≥ 15 years. The estimated case detection rate was 76%. Conclusion Low tuberculosis notification in this mountainous setting is probably a true reflection of low tuberculosis incidence. Possible causes for low incidence in mountainous areas include low transmission rates or altitude-related differences in pathology.