Epidemiological studies, reports from the 1918 influenza pandemic, and clinical observation have associated influenza infection with increased risk for secondary bacterial disease, and especially pneumococcal disease. In fact, up to 6% of invasive pneumococcal disease has been associated with influenza.
The 2009 A/H1N1 influenza pandemic in the United States offered a team of researchers at the National Institutes of Health the opportunity to revisit this association. To do so, the team obtained weekly hospitalization data covering 2003 to 2009 from the State Inpatient Databases of the Healthcare Cost and Utilization Project and calculated the excess pneumococcal pneumonia hospitalization rates for 2009 compared with the baseline calculated from the preceding 6 years.
The results showed that the 2009 pandemic period was associated with a significant increase in pneumococcal pneumonia hospitalizations for everyone between the ages of 5 and 65 years. (Those older than 65 years were spared due to previous exposure to the H1N1 influenza, and those under 5 also experienced a lower impact from H1N1.)
For those aged 5 to 19 years, the pneumococcal pneumonia hospitalization rate increased 1.6-fold overall; for those aged 20 to 39 years, it increased 1.4-fold; and for those aged 40 to 64 years, it increased 1.2-fold. The greatest relative increase was experienced by the youngest group in part because its members had the lowest baseline rate. The greatest absolute increase, on the other hand, was experienced by those aged 40 to 64 years, with an excess of 1.25 pneumococcal pneumonia hospitalizations per 100,000 in population.
The researchers’ study
appears in the February 1, 2012 issue of the Journal of Infectious Diseases
. (Access to full text may require registration.)
Ms. Wick is a visiting professor at the University of Connecticut School of Pharmacy and a freelance writer from Virginia.