Rate and influence of respiratory virus co-infection on pandemic (H1N1) influenza disease.

OBJECTIVES

Many patients with influenza have more than one viral agent with co-infection frequencies reported as high as 20%. The impact of respiratory virus copathogens on influenza disease is unclear. We sought to determine if respiratory virus co-infection with pandemic H1N1 altered clinical disease.

METHODS

Respiratory samples from 229 and 267 patients identified with and without H1N1 influenza respectively were screened for the presence of 13 seasonal respiratory viruses by multiplex RT-PCR. Disease severity between coinfected and monoinfected H1N1 patients were quantified using a standardized clinical severity scale. Influenza viral load was calculated by quantitative RT-PCR.

RESULTS

Thirty (13.1%) influenza samples screened positive for the presence of 31 viral copathogens. The most prominent copathogens included rhinovirus (61.3%), and coronaviruses (16.1%). Median clinical severity of both monoinfected and coinfected groups were 1. Patients coinfected with rhinovirus tended to have lower clinical severity (median 0), whereas non-rhinovirus co-infections had substantially higher clinical severity (median 2). No difference in H1N1 viral load was observed between coinfected and monoinfected groups.

CONCLUSIONS

Respiratory viruses co-infect patients with influenza disease. Patients coinfected with rhinovirus had less severe disease while non-rhinovirus co-infections were associated with substantially higher severity without changes in influenza viral titer.