Updates; February 2008; Scientific American Magazine; by Philip Yam; 1 Page(s)

The number of people living with HIV/AIDS globally has dramatically dropped--not because of an actual drop in the HIV burden but because of better counting methods in India. The Joint United Nations Program on HIV/ AIDS (UNAIDS) and the World Health Organization announced last November that the disease's prevalence in India is 2.5 million--down by more than half from a previous estimate of 5.7 million. A commentary in the December 1, 2007, Lancet explains that previous official counts extrapolated data from large public hospitals. The revised figure derives from a national health survey of 102,000 adults and corroborates earlier findings from a smaller study. The lower estimate means that India will not need to devote as many resources to fight HIV and will not see the same infection rates as sub-Saharan Africa. The numbers support the current prevention strategy of targeting high-risk groups such as sex workers [see "The Prostitutes' Union"; Insights, SciAm, April 2006].

Influenza spreads most readily in winter, but crowding and closed windows have nothing to do with that seasonality. Rather cold air and low relative humidity seem to do the trick. Researchers found that infected guinea pigs kept at five degrees Celsius shed the bug for 40 hours longer than those kept near room temperature. The virus was most stable at relative humidities of 20 to 40 percent: dry air leads to smaller water droplets on which viruses are carried, enabling them to remain airborne for long periods. In the cold, cilia in the respiratory system work more slowly, enabling the virus to spread in the respiratory tract and to disperse in a sneeze or a cough. The study appears in the October 13, 2007, PLoS Pathogens.