The absence of viremia in both patient categories and relatively low viral load in the lung aspirates of the critically ill patients suggest that enhanced replication of the virus may not be an important contributor to the pathogenesis (Figure 1) . The viral load in lung aspirates was independent of fatality. In contrast, among the Spanish patients [10] , 93% and 57% of the mild and critical cases respectively were positive for serum viral RNA, with no significant difference in the viral load. Both studies used CDC primers for real time PCR (http://www. who.int/csr/resources/publications/swineflu/CDCRealtimeR TPCRprotocol_SwineH1Ass-2009_20090428) and the critical cases were bled when already on Oseltamivir treatment, negating sensitivity of the PCR, effect of antiviral therapy or delay in collection of samples to be responsible for different results. The absence of uniform mutations in the fatal casesderived Indian p-H1N1-09 isolates suggests limited/no role of mutant virus in the pathogenesis [11] . Viremia was associated with the outcome of H5N1 infection, 9/11 fatal and 0/5 nonfatal cases being viremic [12] .