Seasonal affective disorder: the miseries of long dark nights?

Many were worried that reliable data could not be collected, but Sir Richard Doll decried the fact that six years into the epidemic we know so little-about crucial aspects ofthe spread of AIDS. In particular there is a desperate need for knowledge about the transmission rate ofHIV infection by vaginal intercourse, and several speakers pleaded for anonymous testing for HIV antibodies of routine blood samples from pregnant women. Sir Richard and others have recently written to the Lancet calling for reconsideration of parliament's rejection of anonymous testing: they point out that "population based screening is . . . an essential accompaniment of mathematical modelling."'" We do at least have monthly figures of newly diagnosed cases of AIDS, and Professor Michael Healy of the London School of Hygiene and Tropical Medicine has used them to predict the number ofnew cases in the short term. A model that gave more weight to recentyears showed that the present doubling rate of cases of AIDS is about 14 months, but data for 1987 have shown the prediction to be slightly too low. None of the models suggest that the epidemic is abating. The doubling time of the epidemic.may be increasing in Europe and the United States, but this is to be expected as those at highest risk tend to become infected early in the epidemic.