Highly Lethal MRSA Pneumonia Associated with Influenza
By Eric Toner, M.D., June 21, 2007
In a recent issue of Mortality and Morbidity Weekly Reports (MMWR) the CDC reported an outbreak of severe community acquired pneumonia (CAP) due to methicillin-resistant Staphylococcus aureus (MRSA).1 All 10 cases occurred in Louisiana and Georgia during December 2006 and January 2007, among previously healthy individuals aged 4 months to 48 years, who had concomitant or recent influenza-like illnesses (6 of 10 had laboratory confirmed influenza). The case fatality rate (CFR) was extraordinarily high at 60%. All of the patients were severely ill: 7 of 10 had multi-lobar infiltrates, and 2 of the 3 patients with single-lobar infiltrates died. The median time from the onset of respiratory symptoms to death was only 3.5 days.
While S. aureus is an infrequent cause of CAP in otherwise healthy individuals, it is a well recognized cause of secondary bacterial pneumonia in the setting of influenza, and when it occurs it is often severe. During the 1968 pandemic in Hong Kong, the CFR for S. aureus-associated pneumonia was 33%, and in many cases, it was associated with death within 24 hours after admission. 2
In recent years, MRSA has been recognized as a possible cause of influenza-associated pneumonia as well. During the 2003-04 influenza season, there were 15 cases of influenza-associated pneumonia due to MRSA, with 4 deaths (CFR of 27%).1
Four of the 10 patients in the recent outbreak were known to have had recent skin or soft tissue infections due to MRSA or were living with someone with a history of such infection. MRSA isolates from 5/6 of the Louisiana cases were available for characterization by CDC. All isolates were resistant to beta-lactams and erythromycin; two had inducible resistance to clindamycin; and two were not susceptible to levofloxacin. All isolates contained genes for the Panton-Valentine leukocidin (PVL) toxin which is associated with necrotizing pneumonia and carried the staphylococcal cassette chromosome mec (SCCmec) type IVa resistance gene cassette which codes for methicillin resistance. Pulsed-field gel electrophoresis analysis revealed that the five isolates had indistinguishable patterns and were designated USA 300-0114.
In the setting of known or suspected influenza, secondary infection due to S. aureus should be considered if there is evidence of pneumonia and particularly if the patient’s condition rapidly progresses. Given its high CFR in the setting of influenza, prompt appropriate antibiotic treatment is indicated if S. aureus pneumonia is suspected. Standard therapy for CAP patients requiring ICU care includes a Β-lactam (cefotaxime, ceftriaxone, or ampicillin-sulbactam) plus either azithromycin or a respiratory fluoroquinolone (moxifloxacin, gemifloxacin, or levofloxacin).3 MRSA pneumonia should be considered as well, particularly if the patient has had recent skin infections or exposure to others with MRSA. If MRSA is suspected, clinicians should add vancomycin or linezolid to the antibiotic regimen.1 If there is evidence of necrotizing pneumonia (cavitation), linezolid may be preferable due to its potential to decrease toxin production.3
Severe Methicillin-Resistant Staphylococcus aureus Community-Acquired Pneumonia Associated with Influenza --- Louisiana and Georgia, December 2006--January 2007. Mortality and Morbidity Weekly Reports (MMWR) 2007;56;325-329 Available online at: http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5614a1.htm.Accessed June 20, 2007
Schwarzmann SW, Adler JL, Sullivan RJ, Marine WM. Bacterial pneumonia during the Hong Kong influenza epidemic of 1968--1969. Arch Intern Med 1971;127:1037--41.
Mandell LA, Wunderink RG, Anzueto A, et al. Infectious Diseases Society of America/American Thoracic Society consensus guidelines on the management of community-acquired pneumonia in adults. Clin Infect Dis 2007;44(Suppl 2):S27--72.