Tuesday, January 12, 2010

Anitbiotics in H1N1 pneumonia

When to Consider the Use of Antibiotics in the Treatment of 2009 H1N1 Influenza-Associated Pneumonia

A difficulty arises when a patient has influenza or influenza with a bacterial superinfection that requires antibiotics.[3]
A recent report showed that bacterial pathogens, including Staphylococcus aureus, were present in 17/53 (32%) of fatal cases of novel H1N1 infection, including 8 in children.[4]
Table 3 summarizes the clinical features of influenza vs influenza with a bacterial superinfection.

Table 3. Detection of Agents of Pneumonia: Influenza vs Influenza + Bacterial Pathogen

Indicator Influenza Influenza + Bacterial Pathogen
Influenza identified Usually found Often found less because later in disease course
Fever Usually found Usually found after a period of defervescence
Respiratory specimen culture Normal flora Pathogen: usually S pneumoniae, S aureus or Group A strep
X-ray Diffuse Lobar consolidation
Onset of respiratory compromise Early: 1-2 days Later: 4-7 days

In regard to antimicrobial selection, these experts recommend coverage for methicillin-resistant Staphylococcus aureus (MRSA) and Streptococcus pneumoniae using a second- or third-generation cephalosporin with the addition of MRSA coverage if there is evidence of necrotizing pneumonia or if a Gram stain or culture of respiratory secretions suggests this pathogen. For outpatients, they suggest amoxicillin-clavulanate or a second- or third-generation cephalosporin.

Commentary. The clinical features suggesting bacterial superinfection are reminders of the well-known report of the 1957-1958 pandemic from NY Hospital-Cornell,[5] when the classic biphasic pattern with typical flu symptoms -- improvement and then rapid deterioration with lobar pneumonia -- was described. The main pathogens then and now are S pneumoniae, S aureus, and group A streptococci. The antibiotics preferred for hospitalized patients with suspected S pneumoniae would be cefotaxime or ceftriaxone. For S aureus (either MRSA or untested), the preference would be for vancomycin dosed to trough levels of 15-20 µg/mL or linezolid (which appears to have better lung penetration).

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