include age distribution, epidemiology, clinical features and overall relative mildness. The late introduction into South Africa appeared, to some extent, to be due to relatively lower air traffic levels and provided a window to observe any further genetic movement in the virus. Phenotypic changes in the virus were certainly not apparent from the clinical and epidemiological observations. Virological characterization is presently under way to determine antigenic drift, resistance, and presence of any virulence markers. Two particular risk groups in South Africa do perhaps need to be highlighted—those involving pregnancy and HIV. Although pregnancy is a well-recognized risk factor in H1N1 (Jamieson et al., 2009; Mangtani et al., 2009), South Africa experienced an unusually high number of women in late pregnancy who succumbed to H1N1. Second, the high rate of HIV positivity in both pregnant and nonpregnant individuals who died (considerably higher than the background HIV positivity in these two groups) needs special attention. In both groups the HIV prevalence was nearly double that of the respective national prevalence rates (Department of Health, 2009). These are, however, preliminary observations and are subject to potentially significant bias. For example, pregnancy may well be a factor that could increase the likelihood of a death being reported because of relatively greater access to a health facility. Also HIV may be artificially high as patients with more advanced disease and the stigma of HIV infection may be more likely to be treated and also more likely to succumb to H1N1. Whether persons living with HIV constitute a risk group for more severe influenza infection in the absence of secondary infection remains to be established (Kunisaki and Janoff, 2009). A study in an HIV-infected pediatric population in South Africa, also failed to demonstrate differences in outcome of influenza infection (Madhi et al., 2002). An understanding of these risk factors is of urgent importance, particularly in countries with a high prevalence of HIV and limited vaccine resources.
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