Endemic diphtheria in Ho Chi Minh City; Viet Nam: A matched case–control study to identify risk factors of incidence

From 1999 to 2004, Ho Chi Minh City (HCMC), Vie Nam reported 401 clinically suspected and 90 laboratory-confirmed diphtheria. To identify risk factors, a matched case–control study was conducted during 2005 and 2006. In total, 88 cases that occurred in 2003 and 2004 and 352 age- and sex-matched controls were studied. No DPT/DT immunisation (odds ratio, 9.9 [95% CI, 1.9–52.3]) and bathing only once a day or less (OR 1.7 [95% CI, 1.0–2.9]) were associated with diphtheria incidence. Estimated vaccine efficacy of three or more DPT/DT doses was 88%. Immunising children with zero-dose status of diphtheria toxoid inoculation, rather than the introduction of booster doses, and the promotion of skin hygiene were considered to be the priority interventions in controlling the endemic diphtheria in HCMC.