Apr 272012
Staph aureus

The CDC announced in its Morbidity and Mortality Weekly Report (MMWR) the sad story of three members of a close-knit Maryland family who all died within days of each other from pneumonia due to seasonal influenza A (H3N2) with methicillin-resistant Staph aureus (MRSA) co-infection.

Three additional family members acquired the same influenza A strain (which was an ordinary circulating strain) and survived; none of them were found to have the MRSA pulmonary co-infection.

One person died at home suddenly; the other patients' presenting symptoms were cough with bloody sputum, fever, and pleuritic chest pain. Chest films showed extensive bilateral opacities. They were treated empirically for bacterial pneumonia; only one got vancomycin, and none got a beta lactamase inhibitor (in accordance with guidelines for community acquired pneumonia treatment). They both had respiratory failure requiring mechanical ventilation and died within a day.

Two of the three had been vaccinated against seasonal influenza. One was on low-dose steroids; all were older than 50, and 2 had multiple comorbidities.

It's believed that these represented a dual initial co-infection, not a superinfection by S.aureus occurring later in the course of influenza. Such bacterial co-infection is well-described and is believed to have caused numerous deaths during the 1918 influenza pandemic.

CDC reports that about 25%–35% of children and adults are colonized with S. aureus, and 1.5% are colonized with MRSA. Health care associated MRSA still causes >80% of invasive MRSA infections. The community-circulating strain, USA300, cause less than 20% of invasive infections (mostly skin and soft tissue infections), but are problematic and dangerous because they are resistant to the beta-lactam antibiotics usually used to treat pneumonia (e.g. ceftriaxone) and many skin infections (e.g. cephalexin or Keflex).

Decolonization / decontamination of MRSA can be done on individuals or family members but its role in preventing pneumonia from MRSA is unknown.

CDC recommends considering treating empirically for both influenza and S.aureus in people "with severe or rapidly worsening disease or with imaging indicative of cavitary or necrotizing pneumonia; this recommendation applies especially when influenza is known to be circulating in the community."

CDC also recommends treating all severe pneumonias empirically with anti-influenza drugs (Tamiflu or Relenza) if influenza is suspected, before testing results are complete (nasopharyngeal or throat swabs, nasal or endotracheal aspirates, nasopharyngeal or bronchial washes, or sputum specimens) and even if >48 hours have elapsed since illness onset. Droplet precautions should be instituted for suspicion of influenza, CDC says.

Prominent experts from the Cochrane Collaboration have challenged CDC's recommendation for empiric use of anti-influenza drugs, saying the data suggest that Tamiflu and Relenza do not reduce complications from severe influenza, and that Roche and GSK are withholding a trove of additional data from their randomized trials that could confirm or refute this suspicion.

Centers for Disease Control and Prevention, Morbidity & Mortality Weekly Report. Severe Coinfection with Seasonal Influenza A (H3N2) Virus and Staphylococcus aureus — Maryland, February–March 2012. April 27, 2012 / 61(16);289-291.

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Watch out for staph coinfections in severe influenza pneumonia (MMWR)