Risk factors for severe outcomes following 2009 influenza A (H1N1) infection

January 01, 0001

Risk factors for severe outcomes following 2009 influenza A (H1N1) infection

Since the start of the 2009 influenza A pandemic (H1N1pdm), the World Health Organization and its member states have gathered information to characterize the clinical severity of H1N1pdm infection and to assist policy makers to determine risk groups for targeted control measures. Data were collected on approximately 70,000 laboratory-confirmed hospitalized H1N1pdm patients, 9,700 patients admitted to intensive care units (ICUs), and 2,500 deaths reported between 1 April 2009 and 1 January 2010 from 19 countries or administrative regions to characterize and compare the distribution of risk factors among H1N1pdm patients at three levels of severity: hospitalizations, ICU admissions, and deaths.

The median age of patients increased with severity of disease. The highest per capita risk of hospitalization was among patients less than 5 y and 5-14 y (relative risk, RR, = 3.3 and 3.2, respectively, compared to the general population), whereas the highest risk of death per capita was in the age groups 50-64 y and greater than or equal to 65 y (RR = 1.5 and 1.6, respectively, compared to the general population). Similarly, the ratio of H1N1pdm deaths to hospitalizations increased with age and was the highest in the greater than or equal to 65-y-old age group, indicating that while infection rates have been observed to be very low in the oldest age group, risk of death in those over the age of 64 y who became infected was higher than in younger groups. The proportion of H1N1pdm patients with one or more reported chronic conditions increased with severity (median = 31.1%, 52.3%, and 61.8% of hospitalized, ICU-admitted, and fatal H1N1pdm cases, respectively). With the exception of the risk factors asthma, pregnancy, and obesity, the proportion of patients with each risk factor increased with severity level. For all levels of severity, pregnant women in their third trimester consistently accounted for the majority of the total of pregnant women. The findings suggest that morbid obesity might be a risk factor for ICU admission and fatal outcome (RR = 36.3).

The researchers concluded: "Our results demonstrate that risk factors for severe H1N1pdm infection are similar to those for seasonal influenza, with some notable differences, such as younger age groups and obesity, and reinforce the need to identify and protect groups at highest risk of severe outcomes."

This will help if there is a future pandemic and, if so, the high-risk groups will become clearer.

For the full abstract, click here.

PLoS Med 8(7):e1001053, 5 July 2011 © The Authors
Influenza A (H1N1) Infection: A Global Pooled Analysis. Maria D. Van Kerkhove, Katelijn A. H. Vandemaele, Vivek Shinde et al. Correspondence to Anthony Mounts: [email protected]

Category: GH. Global Health, R. Respiratory. Keywords: risk factors, outcomes, influenza A, H1N1, infection, global pooled analysis, journal watch.
Synopsis edited by Dr Stephen Wilkinson, Melbourne, Australia. Posted on Global Family Doctor 22 July 2011

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