Survival of group A streptococci in dried human blood

The resurgence of streptococcal infections in the USA and Europe and their high incidence in other parts of the world prompted an examination of the survival and maintenance of virulence of group A streptococci. Human blood containing group A streptococci was placed on small pieces of sterile paper towelling and allowed to dry at room temperature. At periods of 2, 8, 15 and 20 weeks later, the paper with the dried blood was placed in Todd-Hewitt broth and incubated at 37 degrees C overnight. All the samples tested at 2 weeks grew in broth, and with only one exception, grew in fresh human blood provided by five donors. At 8 weeks only two of the 10 strains failed to grow in broth; seven of the eight viable cultures also grew in blood. At 15 and 20 weeks after drying the eight cultures were still viable. Since seven were able to grow in fresh blood as well as in broth it is assumed that their virulence factor(s) had been retained.