What is the mortality and morbidity of influenza pneumonia?

Updated: Mar 24, 2021
  • Author: Zab Mosenifar, MD, FACP, FCCP; Chief Editor: John J Oppenheimer, MD  more...
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Influenza virus represents a common cause of pneumonia in the adult population, affecting 4-8% of healthy adults. Rates have been 10-20% during outbreaks and as high as 50% during epidemics. Morbidity and mortality rates related to influenza pneumonia in both the general population and in selected groups (eg, patients with chronic diseases, the elderly) are substantial.

The highest rates of hospitalization for influenza occur in preschool-aged children and in the elderly population. During outbreaks, the hospitalization rates are 27.9 cases per 10,000 persons younger than 5 years and 55 cases per 10,000 persons older than 65 years. Between 1972 and 1992, 426,000 deaths related to influenza pneumonia were reported in United States. Individuals 85 years or older were 16 times more likely than those aged 65-69 years to die from influenza.

Also in contrast with seasonal influenza, mortality was higher in younger patients with H1N1 influenza, with 87% of deaths and 71% of severe pneumonia in the age group of 5-51 years. [44] The higher mortality in patients younger than 60 years may reflect this cohort’s lack of exposure to the 1957 (and earlier) H1N1 influenza strains. Exposure to those early strains may have conferred some immunity in the older population. Also of interest is a report that identified obesity as a possible risk factor for more severe disease/mortality. [46]

As of February 2010, the CDC had estimated that 8,330 to 17,160 H1N1-related deaths occurred between April 2009 and January 16, 2010 in the United States, [47] and the World Health Organization (WHO) has estimated that, worldwide, at least 16,226 deaths have been directly attributable to H1N1. [48]

The H5N1 avian influenza seems to be more virulent than seasonal influenza, with a 59% mortality rate in cases reported thus far. [30] The median time from disease onset to death is nine days. The majority of these patients had no underlying medical problems.

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