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H1N1 (Swine Flu): A Deeper Look at the Numbers

May 7, 2009

There is a phenomenal amount of research being conducted in real time assessing the impact of the current outbreak of H1N1.  These investigative teams include infectious disease physicians, registered nurses and epidemiologists. They are all trying to make sense of the numbers and statistics being reported from around the world with the goal of providing a clearer picture of the evolving epidemic.

A web edition of the New England Journal of Medicine (NEJM) shares some interesting data from the United States in the article, “Emergence of a Novel Swine-Origin Influenza A (H1N1) Virus in Humans.”

Epi Chart

1. Of a total of 642 confirmed cases in the US, identified April 15 to May 5, the hospitalization status was known for only 399 of the confirmed cases.

  • Of the 399, 36 or 9% required hospitalization.
  • Of the 36, data was available for only 22 cases.
  • Of the 22 cases for which there was data, 12 (55%) had characteristics that conferred an increased risk of severe seasonal influenza, 9 (41%) had chronic medical conditions, 11 (50%) had radiologically confirmed pneumonia, 8 (36%) required admission to an intensive care unit, 4 (18%) had respiratory failure requiring mechanical ventilation, and 2 died.
  • Of the 22 hospitalized patients for whom data were available 4 (18%) were children under the age of 5 years
  • Of the 22, fourteen patients (74%) were treated with oseltamivir (Tamiflu) after admission to the hospital.
  • Of the 22 hospitalized patients, 18 (82%) had recovered from the acute illness, 2 (9%) patients remain critically ill with respiratory failure, and 2 have died.

2. 60% of patients with confirmed infections were 18 years of age or younger.

3. Continued identification of new cases in the US and elsewhere, indicated sustained transmission from person to person.

Epi Map

4. Disease transmission is thought to occur through the distribution of large droplets and possibly small particle droplet nuclei expelled when a person coughs or sneezes. There remains a potential for transmission through contact with inanimate objects (fomites) that are contaminated with respiratory and gastrointestinal material.

Everyone should assume that any bodily fluids at this point may contain virus particles – therefore the education about hand/cough hygiene, hand washing  and contact cleaning of highly touched surfaces has never been so important.  Check out the NJEM site for interesting clinical and policy articles on H1N1.

Source: New England Journal of Medicine  http://h1n1.nejm.org/

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