New Clinical Model Identifies H1N1 Influenza-Related Pneumonia

A diagnostic model based on five clinical criteria effectively distinguishes H1N1 influenza-related pneumonia from inter-pandemic community-acquired pneumonia (CAP), reports a new study.

Researchers at Nottingham University Hospitals NHS Trust (United Kingdom) studied data collected by the UK Influenza Clinical Information Network (FLU-CIN) on 1,046 adults admitted to 75 hospitals with confirmed H1N1 influenza, between May 2009 and January 2010. Of these, 254 were found to have H1N1 influenza-related pneumonia on admission. Clinical and epidemiological information from these 254 patients were compared with that from 648 adults with CAP who were admitted to hospital between September 2008 and June 2010, excluding those admitted during the period of the pandemic.

The results of the study showed that although both groups had similar levels of in-hospital mortality (11.4% for the H1N1 cohort, compared to 14.0% in the CAP cohort), they differed significantly on a number of clinical characteristics. Analysis revealed five clinical criteria that distinguished between the cohorts; these included age younger than 65 years, bilateral radiographic change, mental orientation (i.e., awareness of time, place, and person), a low leucocyte count, and body temperature of over 38 °C. By assigning a score of one point for each of these five clinical criteria, the team found that a score of 4 or 5 gave a positive likelihood ratio of 9.0 for predicting H1N1 influenza-related pneumonia, while a score of 0 or 1 gave a positive likelihood ratio of 75.7 for excluding it. The study was published in the March 2011 issue of Thorax.

"A model based on five simple clinical criteria… allows the early discrimination of H1N1 influenza-related pneumonia from CAP following hospital admission and confers confidence to the instigation of early empirical antiviral therapy,” concluded lead author consultant respiratory physician Wei Shen Lim, MD, and colleagues of the department of respiratory medicine.

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Nottingham University Hospitals NHS Trust