To the Editor.—
We appreciate Drs Murphy and Osterholm sharing data from their recent abstracts on rates of secondary disease in day-care center contacts of a case of Hemophilus influenzae disease.1 They interpret these findings as suggesting that, in analyzing the impact of rifampin for prevention of secondary disease in the collaborative study,2 one should consider day-care centers and households separately. However, there is an appropriate way to analyze the data from the collaborative study that takes into consideration the possibility of different rates of secondary disease, as well as the small numbers in some of the categories. This exact test for combining 2×2 tables computes the overall efficacy of rifampin and its statistical significance while analyzing household contacts separately from day-care classroom contacts.3 Stratified for site of exposure, the effect of rifampin was significant in the group of contacts as a whole (P=.028) and in
Band JD, Fraser DW, Hightower AW, Broome CV. Prophylaxis of Hemophilus influenzae Type b Disease. JAMA. 1984;252(23):3249–3250. doi:10.1001/jama.1984.03350230011007
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