Invasive bacterial infections following influenza: a time-series analysis in Montréal, Canada, 1996-2008
R Allard1, M Couillard, P Pilon
1Public Health Department, Montréal Health and Social Services Agency. rallard@santepub-mtl.qc.ca
Background:
Shared seasonal patterns, such as between influenza and some respiratory bacterial infections, can create associations between phenomena not causally related.
Objectives:
To estimate the association of influenza with subsequent bacterial infections after full adjustment for confounding by seasonal and long-term trends.
Methods:
Time series of weekly counts of notified cases of invasive infections with Haemophilus influenzae, Neisseria meningitidis, Streptococcus pneumoniae and Streptococcus pyogenes, in Montréal, Canada, 1996-2008, were modelled by negative binomial regression, with terms representing seasonal and long-term trends and terms for numbers of positive laboratory tests for influenza A and B.
Results:
The associations of S. pneumoniae, H. influenzae and N. meningitidis with influenza disappeared after seasonal terms were added to the model. However, the influenza B count remained associated with the S. pyogenes counts for the same week and the following week: S. pyogenes incidence rate ratios were 1.0376 (95% CI: 1.0009-1.0757) and 1.0354 (0.9958-1.0766), respectively, for each increase of 1 in the influenza count.
Conclusions:
Influenza B accounts for about 8 percnt; of the incidence of invasive S. pyogenes infections, over and above any effect associated with modellable seasonal and long-term trends. This association of influenza B with S. pyogenes infections can be attributed largely to the years 1997, 2001, 2007 and 2008, when late peaks in influenza B counts were followed by peaks in S. pyogenes notifications. This finding reinforces the case for universal immunization against influenza, as partial protection against the 'flesh eating disease'.
Insights
Influenza B infections are linked to Streptococcus pyogenes, a cause of invasive bacterial infections. This association highlights the importance of influenza vaccination for preventing severe bacterial complications.
Area of Science:
- Infectious Disease Epidemiology
- Public Health Microbiology
- Respiratory Virus Research
Background:
- Shared seasonal patterns can create spurious associations between influenza and bacterial infections.
- Distinguishing true causal links from seasonal confounding is crucial for public health interventions.
Purpose of the Study:
- To quantify the association between influenza and subsequent invasive bacterial infections.
- To adjust for seasonal and long-term trends to isolate specific influenza-bacterial infection links.
Main Methods:
- Time series analysis of weekly invasive bacterial infection cases (Haemophilus influenzae, Neisseria meningitidis, Streptococcus pneumoniae, Streptococcus pyogenes) in Montreal (1996-2008).
- Negative binomial regression modeling incorporating seasonal/long-term trends and influenza A/B laboratory test data.
Main Results:
- Associations between influenza and S. pneumoniae, H. influenzae, and N. meningitidis were eliminated after accounting for seasonality.
- Influenza B showed a persistent association with S. pyogenes, with incidence rate ratios of 1.0376 and 1.0354 for concurrent and subsequent weeks, respectively.
Conclusions:
- Influenza B contributes approximately 8% to invasive S. pyogenes infections, independent of seasonal trends.
- Specific years with late influenza B peaks correlated with S. pyogenes outbreaks.
- Findings support universal influenza immunization to mitigate invasive S. pyogenes (flesh-eating disease) risk.
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