To the Editor.—
Mann et al1 claim that their study in Zaire "provides evidence against horizontal HTLV-III/LAV [human T-cell lymphotropic virus type III/lymphadenopathy-associated virus] transmission among household members." Actually, their data indicate the opposite. They found nine of 186 household contacts (excluding spouses) of patients with the acquired immunodeficiency syndrome (AIDS) to be seropositive, compared with only two of 128 household contacts of controls who were seronegative and matched to the AIDS cases by age and sex. The numbers may be small, but they are not comforting. The authors report a prevalence ratio estimate of 3.1, with a 95% confidence interval of 0.7 to 13.3. The authors state that "seroprevalence did not differ significantly between case-and control-household contacts," and claim that the data provide support for the null hypothesis. The confidence interval, however, indicates that the data are compatible with a wide range of values for the prevalence ratio.