Difficulties of interpreting PPD reactions of women living in Madang, Papua New Guinea

Abstract Malaria surveys in Madang, Papua New Guinea, previously distinguished 2 populations of women with significantly different spleen rates and immune responses to malaria. Differences between the high (HS) and low (LS) spleen rate groups suggested a defect in cellular immunity in the HS group. This paper reports a survey of purified protein derivative (PPD) responses in a sample of HS and LS women. Eighty-eight of 162 women were PPD positive (reaction size > 5 mm). There was a marked difference in the range and size of PPD reaction between the HS and LS groups. Mean size in the LS group was 20·7 mm and in the HS group it was 12·1 mm ( P = 0·02). Failure to show differences in other indicators of specific malaria immunity indicated that the difference in PPD response was not the result of malaria-specific cell-mediated immune suppression. Many women were PPD non-responders in spite of evidence of multiple bacillus Calmette-Guerin (BCG) vaccination scars. There was no difference between HS and LS groups in the level of non-response to PPD. The results confirm an early tuberculosis survey indicating that New Guineans rapidly lose PPD reactivity to BCG vaccination. Ability to maintain a PPD response, and the quality of response, may vary according to sex and genetic background.