H1N1 Flu and Blood Clots

A recent report appeared in the American Journal of Roentgenology (1) describing a small number of patients with H1N1 infection who were severely ill, hospitalized in an intensive care unit, and found to have pulmonary emboli (PE or blood clots in the lungs) during the course of their illness.  Questions have since risen about the risk of PE in the setting of H1N1 infection.
 
It is well known that severely ill, hospitalized patients, especially in an intensive care setting, are at risk of developing blood clots in their legs (deep vein thrombosis or DVT) and pulmonary emboli.  Hospitalization itself, with bed rest and complex medical illnesses, is a risk for DVT, especially in patients who may have other inherent risk factors.  The patients in this report, besides being quite ill, had numerous other risk factors for DVT and PE, and it cannot be said with any certainty that H1N1 infection is a major risk factor for such clots.  Further discussion of these issues can be found in an article about these and other severely ill patients with H1N1 virus infection in CDC’s Morbidity and Mortality Weekly Report (2).
 
If you have a history of a blood clot or you have been told by your doctor that you are at risk for blood clots, it is important to speak with your physician about such risks and ask about the benefits of medications (“blood thinners”) that can prevent such clots.
 
With respect to H1N1 (and seasonal) flu, CDC guidance for who should be vaccinated and other measures of prevention (http://www.cdc.gov/H1N1FLU) should be followed in consultation with your physician or other health professionals.
 
For more reading:
(1) Agarwal PP, Cinti S, Kazerooni EA. Chest radiographic and CT findings in novel Swine-Origin InfluenzaA (H1N1) virus infection. American Journal of Roentgenology 2009;193:1-6.
 
(2) Intensive-care patients with severe novel influenza A (H1N1) virus infection July 10, 2009;
MMWR 58:749-752.  http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5827a4.htm
 
10.21.09

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