This article is more than 5 years old. Information may no longer be current.
Further research needed to explain variation in invasive pneumonia, RSV link
Zhou H. Emerg Infect Dis. 2012;doi: Embargoed until 12pm Wednesday.
Click Here to Manage Email Alerts
Invasive pneumococcal pneumonia was significantly associated with influenza and respiratory syncytial virus throughout the course of five out of 11 influenza seasons, new findings suggest.
The researchers also found that association strength was higher when influenza A (H3N2) was the predominant strain, whereas there was no significant association in any of the seasons in which H3N2 was not predominant.
Between October and May of US influenza seasons from 1994 to 2005, researchers pooled weekly data from the Atlanta area. For five of 11 seasons, they found that invasive pneumococcal pneumonia was significantly associated with influenza and respiratory syncytial virus (RSV).
However, significant variations in the intensity of association of invasive pneumococcal pneumonia incidence with influenza virus and RSV were observed for the remaining seasons. Therefore, the researchers said data from one season or combined data from several seasons are inconsistent considering the variability observed.
Disclosure: The researchers report no relevant financial disclosures.
The relationship between viral respiratory infection (especially influenza) and concomitant or second bacterial infection is well entrenched in our thinking, but as indicated by Zhou et al, the evidence is perhaps not as clear as we might have perceived. Potential mechanisms for synergies between viral and bacterial infection include: virus destruction of respiratory epithelium, which may increase bacterial adhesion; influenza virus neuraminidase activity, which might also enhance bacterial adherence; inflammatory responses to viral infection that may upregulate expression of molecules utilized as receptors by bacteria; and virus-induced, immunosuppression-promoting bacterial superinfections. Although an association with influenza and second bacterial pneumonia is well recognized, Zhou et al have added to our understanding of a specific magnitude of effect associating the type of influenza with invasive pneumococcal infection while adjusting for other factors such as cold temperatures, lack of sunshine, and rainy and snowy weather. They have observed a substantial association during 5 seasons when influenza A virus H3N2 was predominant and not when other strains were predominant.
The observation of higher complication rates associated with H3N2 strains of influenza has been reported previously. Thompson et al. reported estimated rates of influenza-associated hospitalizations were highest during seasons in which influenza A H3N2 viruses predominated, followed by B and A H1N1. One explanation of these findings and those of others showing a higher association with H3N2 strains is related to excess neuraminidase expression of H3N2 compared with H1N1. In a mouse model, Peltola et al have established that viral neuraminidase is an important factor in viral-bacterial synergism. Not only is neuraminidase activity needed by influenza for release of virus from cells, but it also promotes adherence and invasion of S. pneumoniae.
The findings of Zhou et al are important for anticipating and predicting potential morbidity and mortality with each influenza season depending on the predominant strain. In addition the significance of excess neuraminidase has implications for utilization of neuraminidase-inhibiting agents.
– Thomas M. File Jr., MD
Infectious Disease News Editorial Board member
Disclosure: Dr. File reports no relevant financial disclosures.
For more information:
- Peltola VT. J Infect Dis. 2005;192:249-257.
- Thompson WW. JAMA. 2004;292:1333-1340.
 |
Follow InfectiousDiseaseNews.com on Twitter. |