Bacterial Coinfection May Have Contributed to H1N1 Deaths

From Medscape Medical News
Laurie Barclay, MD

September 30, 2009 — Bacterial coinfection with Streptococcus pneumoniae may have contributed to deaths in the United States from 2009 H1N1 influenza, according to the results of a study reported online first in the September 29 issue of the Morbidity and Mortality Weekly Report. The Centers for Disease Control and Prevention (CDC) are therefore urging pneumococcal vaccination when indicated.

"Our influenza season is off to a fast start and unfortunately there will be more cases of bacterial infections in people suffering from influenza," CDC Epidemiologist Matthew Moore, MD, said in a news release. "It's really important for people, especially those at high risk for the serious complications from influenza, to check with their provider when they get their influenza vaccine about being vaccinated against pneumococcus."

In an analysis of lung tissue specimens from 77 confirmed fatal US cases of 2009 H1N1, in which deaths occurred from May 1 to August 20, 2009, bacterial coinfections were present in 22 (29%) cases. These fatal cases were defined as influenza-like illness or postmortem findings suggesting viral pneumonia and laboratory-confirmed 2009 pandemic influenza A (H1N1) virus infection by real time reverse transcriptase–polymerase chain reaction.

Of the 22 cases with bacterial coinfection, 10 were caused by S pneumoniae, 7 by S aureus, 6 by S pyogenes, 2 by S mitis, and 1 by Haemophilus influenzae. In 4 cases, there were multiple pathogens. Median age was 31 years (range, 2 months – 56 years), and half were men. The cases were reported from California, Hawaii, Illinois, New Jersey, New York, Texas, Utah, and Virginia.

Of the 21 patients with known previous medical history, 16 had underlying medical conditions associated with increased risk for influenza-associated complications, and 15 had indications for vaccination with 23-valent pneumococcal polysaccharide vaccine.

The CDC is recommending that:

pneumococcal conjugate vaccine be given to all children younger than 5 years, as per current guidelines, and
all persons aged 65 years and older, as well as those aged 2 to 64 years with high-risk conditions, receive the 23-valent pneumococcal polysaccharide vaccine, as described on the CDC's Web site.

Limitations of this report are that the cases do not come from a systematic sample and might not be representative of all pandemic H1N1 deaths or all pandemic H1N1 deaths associated with bacterial pneumonia. Not all potential bacterial pathogens were evaluated, patient information was limited, and evaluation of bacterial coinfections was performed at autopsy.

"The findings in this report also underscore the importance of managing patients with influenza who also might have bacterial pneumonia with both empiric antibacterial therapy and antiviral medications," the editors conclude. "In addition, public health departments should encourage the use of pneumococcal vaccine, seasonal influenza vaccine, and, when the vaccine becomes available, pandemic influenza A (H1N1) 2009 monovalent vaccine."

Morb Mortal Wkly Rep. Published online September 29, 2009.