Objective: To determinate the relative importance of state of nutrition and intensity of exposure for clinical severity of chickenpox in a developing country.

Methods: A prospective household study was performed in a semi-urban area in Bissau, the capital of Guinea-Bissau, between December 1994 and June 1995. Antibodies were measured in the acute and the convalescence phase to assess validity of clinical diagnoses. The clinical severity of infection was assessed by number of pox, fever response and skin infections. Severity was compared for index cases, i.e. the first case in the house, and secondary and tertiary cases infected following exposure at home.

Result: Chickenpox was diagnosed in 165 persons. The clinician's and the mothers' diagnoses corresponded well with the serological results. Median age was 36 months (range 3 months to 30.3 years). There was no correlation between nutritional status measured by arm-circumference and severity of infection. The number of pox was higher for secondary cases than for index cases (median 106 vs. 89, P<0.01), the difference being more pronounced for girls (P=0.018) than for boys (P=0.575). The risk of skin infection as a complication was correlated with the number of pox (P<0.001).

Conclusion: Chickenpox was recognised correctly by Guinean mothers. The age distribution in Guinea-Bissau resembled the pattern in developed countries. The intensity of exposure was a major determinant of severity, especially for girls.