Zhou H. Emerg Infect Dis. 2012;doi: Embargoed until 12pm
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
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
Thomas M. File, Jr., MD
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
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
For more information:
- Peltola VT. J Infect Dis. 2005;192:249-257.
- Thompson WW. JAMA. 2004;292:1333-1340.