Editor's note: This story was revised Sep 29 to correct a detail about when pneumonia cases were diagnosed.

Sep 28, 2009 (CIDRAP News) – Almost one third of a group of patients who died in the past 4 months from H1N1 influenza had bacterial infections that complicated their illnesses, the Centers for Disease Control and Prevention (CDC) said today in a conference call with healthcare providers. But the agency cautioned against applying that ratio to all cases of H1N1, saying the death records it reviewed were submitted by hospitals and medical examiners and did not represent a statistically valid sample.

Nevertheless, the 22 cases (among 77 deaths confirmed to be from H1N1) emphasize that bacterial co-infections are playing a role in the ongoing pandemic, something that was not clear at first, the CDC's Dr. Matthew Moore said on the call.

"During the early part of this pandemic, evidence of bacterial co-infection was pretty much absent," Moore said during the call, part of the CDC's "Clinician Outreach and Communication Activity" program. That "may have led to the perception that bacterial co-infection is playing only a limited or maybe even no role in this current pandemic. . . . [But] bacterial pneumonia may be contributing to influenza-associated mortality in a manner similar to that in previous pandemics."

The 77 patients whose deaths and autopsy data were evaluated by the CDC are expected to be described in a forthcoming article in the agency's Morbidity and Mortality Weekly Report. They ranged in age from 2 months to 84 years, with a median age of 39. Nine out of 10 had some underlying condition that made them vulnerable to the severest effects of flu, such as obesity, cardiac disease, asthma, diabetes, or HIV infection. Three were women in the last trimester of pregnancy.

All appear to have been severely ill: 63% received influenza antivirals and 81% were put on ventilators. Pneumonia was diagnosed before death in 39% of the cases.

The 22 patients (29%) who were confirmed to have bacterial complications were infected with Streptococcus pneumoniae (pneumococcus), Staphylococcus aureus, Group A strep, and Haemophilus influenzae. (Four were infected with more than one bacterial type.) Five of the seven S aureus infections involved methicillin-resistant (MRSA) strains.

Moore said the CDC is especially concerned that 16 of the 22 fall into categories of people who are recommended to receive pneumococcal vaccine because of their age or underlying chronic conditions. The agency received limited clinical data on the cases and thus could not say whether they received the vaccine—but it is well-known, Moore said, that only 16% of Americans who should receive pneumococcal vaccine do so.

In response, the CDC is urging people at high risk for pneumococcal disease to be vaccinated, Moore said: "If you add up all the people in the United States who should have received pneumococcal polysaccharide vaccine but have not yet received it, that totals 70 million individuals. We have a terrific opportunity here to prevent additional pneumococcal disease."

See also:

CDC recommendation for pneumococcal vaccination for adults

http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5934a3.htm

CDC recommendation for pneumococcal vaccination for children

http://www.cdc.gov/mmwr/PDF/rr/rr4909.pdf