H1N1 Influenza
H1N1 influenza (formerly referred to as the swine flu) first made its appearance last April. By early June, the virus had spread to 74 countries and infected more than 30,000 people. On June 11, the World Health Organization raised the alert level to the a pandemic, or phase 6.

In the U.S., cases of H1N1 have been reported in all 50 states. Because the H1N1 flu is so widespread, the CDC no longer tracks individual cases. However, hospitalizations and deaths are still being recorded. Between August 30th and September 26th, more than 16,170 Americans have been hospitalized for flu complications and 1,379 have died (For updates, go to: http://www.cdc.gov/flu/weekly). 99 percent of flu cases still being reported are H1N1.

ARDS
A serious complication of pneumonia is acute respiratory distress syndrome (ARDS). This condition affects the tiny air sacs (the alveoli) in the lungs, where oxygen is normally absorbed into the bloodstream. The sacs collapse or become filled with fluid, interfering with the ability of the lungs to take in oxygen. As a result, the body’s tissues don’t get enough oxygen. Organs may not function well or, in some cases, may fail. Patients may require a ventilator or ECMO (like a heart-lung bypass machine to oxygenate the blood) and intensive care treatment for many weeks.

The National Heart, Lung and Blood Institute estimates, annually, there are about 190,000 cases of ARDS in the U.S. About 30 percent of patients die. Some of those who survive are left with permanent lung damage.

H1N1 and ARDS
In a small observational study, Lena Napolitano, M.D., Critical Care Surgeon with the University of Michigan Health System, looked at 10 patients admitted to a surgical intensive care unit for severe ARDS associated with H1N1 infection. None of the 10 patients had any evidence of secondary bacterial infection, typically an important cause of severe illness in flu patients. The researchers also noted some other unusual characteristics of these patients. Normally, flu-related pneumonia affects older people, the very young and those with weak immune systems. But the patients with ARDS were all middle aged, ranging from 21 to 53 years old. Nine of the ten patients were obese; seven were extremely obese. Half the patients had developed lung clots.

Napolitano says the cases highlight the need for doctors to be aware that patients coming into the hospital for treatment of ARDS may also have H1N1 influenza and should receive antiviral medication. Doctors should also be aware of the potential for severe complications among those who are extremely obese, though the reasons for this link are unclear.

A new report from the CDC found secondary bacterial lung infections are now becoming more prevalent in H1N1. Roughly 29 percent of patients who died of H1N1 complications between May and August had secondary bacterial infections. Thus, researchers now say doctors should now also consider the need for antibiotics in patients with H1N1-associated pneumonia.

AUDIENCE INQUIRY
For up-to-date information on the H1N1 pandemic flu, go to http://www.cdc.gov/h1n1flu

For general information on pneumonia or ARDS:
American Lung Association, http://www.lungusa.org
ARDS Support Center, www.ards.org
National Heart, Lung and Blood Institute, http://www.nhlbi.nih.gov

BIBLIOGRAPHY
“Bacterial Coinfections in Lung Tissue Specimens from Fatal Cases of 2009 Pandemic Influenza A (H1N1) – United States, May-August 2009,” MMWR: Morbidity and Mortality Weekly Report, October 2, 2009, Vol. 58, No. 38, pp. 1071-1074.

Gupta, Ravindra, et al., “Bacterial Pneumonia and Pandemic Influenza Planning,” Emerging Infectious Diseases, August 2008, Vol. 14, No. 8, pp. 1187-1192.

Ho., Y., et al., “Prognostic Factors for Fatal Adult Influenza Pneumonia,” Journal of Infection, June 2009, Vol. 58, No. 6, pp. 439-445.

“Intensive-Care Patients with Severe Novel Influenza A (H1N1) Virus Infection – Michigan, June 2009,” MMWR: Morbidity and Mortality Weekly Report, July 17, 2009, Vol. 58, No. 27, pp. 749-752.

Kuiken, Thijs, and Jeffrey Taubenberger, “Pathology of Human Influenza Revisited,” Vaccine, September 12, 2008, Vol. 26, No. 4, pp. D59-D66.

Memoli, Matthew, et al., “Pandemic and Seasonal Influenza,” Drug Discovery Today, July 2008, Vol. 13, No. 13-14, pp. 590-595.

Taubenberger, Jeffrey, and David Morens, “The Pathology of Influenza Virus Infections,” Annual Review of Pathology, 2008, Vol. 3, pp. 499-522.

Research compiled and edited by Barbara J. Fister