MRSA main cause of S. aureus community pneumonia during flu season

By Anthony J. Brown, MD

NEW YORK (Reuters Health) - During the 2006 to 2007 influenza season in the US, 79% of community-acquired pneumonia cases caused by Staphylococcus aureus were due to MRSA, according to a report in the June 3rd online issue of the Annals of Emergency Medicine.

Many of the cases occurred with or after influenza and often involved otherwise healthy young people, according to the report. Just over half of the cases proved fatal.

"I think the most interesting findings were the large proportion (of cases) that were MRSA, the large number that were not empirically treated for this organism and the potential association between co-infection with influenza and a worsened outcome," lead author Dr. Alexander J. Kallen, from the Centers for Disease Control and Prevention in Atlanta, told Reuters Health.

A number of S. aureus community-acquired pneumonia cases reported to public health authorities in early 2007 led Dr. Kallen's team to seek out additional case reports nationwide, in an effort to better characterize the cases seen during the 2006 to 2007 influenza season. The study period ran from November 1, 2006 to April 30, 2007.

A total of 51 cases were identified in 19 states, of which 47 had known susceptibility results, the authors note. The median patient age was 16 years; 44% had no history of pertinent medical problems. Twenty-four (51%) patients died at a median of 4 days after symptom onset.

Thirty-seven (79%) of the 47 cases were due to MRSA, the report indicates. Just 16 (43%) of MRSA-infected patients were treated empirically with recommended antimicrobial agents.

In 22 (47%) of the 47 cases, the S. aureus infection arose during or after a viral infection. Influenza infection was confirmed in 11 (33%) of 33 patients who were tested.

"The main take-home messages for clinicians," Dr. Kallen said, "are that this disease (S. aureus pneumonia with onset in the community, including MRSA) is seen during the winter months, it can be severe, and it should be considered in people presenting with pneumonia during the winter."

He added, "Obviously consideration should be given to influenza vaccination for those who may wish to increase their chances of avoiding influenza and its potential complications."