Streptococcus pneumoniae is a leading cause of otitis media, sinusitis, pneumonia, sepsis, and meningitis in children. Although it is well known that prior respiratory virus infections enhance the severity of bacterial infections, the effect of influenza on transmission of S. pneumoniae has not been studied. We infected groups of weanling ferrets with influenza virus strain A/Sydney/5/97 (H3N2) or a pneumococcal strain engineered to express luciferase (SME33, type 19F) 72 hours before placing them in contact overnight in various combinations in (1) the same cage, (2) in a different cage in the same cubicle ≈ 3 feet apart, or (3) in a different cage in a different cubicle ≈ 10 feet apart. Animals then had daily nasal washes for quantitation of influenzal and pneumococcal titers, as well as imaging for bioluminescence indicative of invasive infection. S. pneumoniae transmitted from ferrets infected with pneumococcus alone to uninfected ferrets in (1) 4 of 4 same cage contacts, (2) 4 of 4 same cubicle contacts, and (3) 0 of 4 different cubicle contacts. Twenty-five percent (2/8) of the infected contacts developed either otitis media, sinusitis, or both. Preinfection of the donor ferrets with influenza virus did not alter the transmission dynamics. When recipient ferrets were preinfected with influenza prior to exposure to the ferrets shedding pneumococcus, however, all contacts were infected (12/12), significantly higher titers of bacteria were recovered, and 50% (6/12) of infected contacts developed otitis media, sinusitis, or both. These data suggest that influenza infection increases the likelihood of being infected upon natural exposure to S. pneumoniae and enhances the incidence of secondary complications but does not increase transmission from the coinfected donor.
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