Pulmonary infection due to methicillin-resistant Staphylococcus aureus

Health care-associated Staphylococcus aureus pneumonia

INTRODUCTION

While Staphylococcus aureus is an uncommon but serious cause of traditional community-acquired pneumonia (CAP), it is a predominant cause of nosocomial pneumonia in addition to the unique clinical entity of health care-associated pneumonia (HCAP). A cohort of bacteremic S aureus pneumonia cases was reviewed to determine the role of HCAP among the cohort, and to assess for differences between CAP and HCAP.

PATIENTS AND METHODS

Bacteremic S aureus pneumonia cases were identified from a prospective study of all patients diagnosed with CAP who presented to hospitals in Edmonton, Alberta, between November 2000 and November 2002. These cases were subsequently reviewed retrospectively. Demographic, clinical and microbiological data were obtained, and patients were classified as having CAP or HCAP. Relatedness of isolates was determined by pulsed-field gel electrophoresis analysis in conjunction with epidemiological information.

RESULTS

There were 28 cases of bacteremic S aureus pneumonia identified. Fifty-seven per cent were reclassified as having HCAP, and 43% remained classified as having CAP. The CAP cohort was significantly younger than the HCAP cohort (mean age 49.0+/-23.7 years versus 67.8+/-18.6 years; P=0.035) with higher rates of intravenous drug use (50% versus 0%; P=0.002). Long-term care facility residence (44%) was common in the HCAP cohort. The HCAP cohort presented with more severe illness, having a higher mean pneumonia severity index score (143.1+/-41.1 versus 98.2+/-54.6; P=0.028), and despite fewer embolic complications, there was a trend toward a significantly higher mortality rate (31% versus 0%; P=0.052). Two community-acquired isolates cultured in the setting of intravenous drug use were methicillin-resistant, and no isolates were positive for Panton-Valentine leukocidin. There was evidence of relatedness involving 44% of the HCAP isolates by pulsed-field gel electrophoresis analysis.

CONCLUSION

HCAP accounts for a significant number of cases that, when using traditional definitions, would be classified as CAP. Severity of illness and mortality was excessive within the HCAP group. There was evidence of relatedness and spread of common strains in the HCAP cohort. The present study supports recommendations for treatment guidelines directed toward the entity of HCAP and the empirical coverage of S aureus among certain high-risk groups.

Successful unrelated BMT in a patient with Kostmann syndrome complicated by pre-transplant pulmonary 'bacterial' abscesses

Kostmann syndrome, severe congenital neutropenia, is often associated with life-threatening bacterial infections. A 5-year-old girl with Kostmann syndrome developed pulmonary abscesses. She was refractory to granulocyte colony-stimulating factor and antibiotics. She underwent unrelated HLA-matched BMT. Myeloablative conditioning consisted of 12-Gy TBI with lung shielding, antithymocyte globulin, etoposide, and cyclophosphamide. After successful engraftment, the pulmonary abscesses resolved by day 75 post-transplant. Although the option of transplantation is not established in the setting of unrelated HLA-matched BMT in Kostmann syndrome, this case may provide useful information. Furthermore, pre-transplant pulmonary bacterial abscesses may not be a contraindication for BMT in some patients with Kostmann syndrome.

Bacteremic pneumonia due to Staphylococcus aureus: A comparison of disease caused by methicillin-resistant and methicillin-susceptible organisms

We performed a prospective study of all patients with bacteremic pneumonia due to Staphylococcus aureus over a period of 6 years during an outbreak of methicillin-resistant S. aureus (MRSA). Patients with bacteremic pneumonia due to MRSA (32 cases) or methicillin-susceptible S. aureus (MSSA; 54 cases) were compared. The patients with MRSA pneumonia were older and were more likely than those with MSSA pneumonia to have predisposing factors for acquisition of the infection. There were no differences in clinical findings, radiological pattern, or complications in clinical evolution among patients with MRSA and MSSA pneumonia. Mortality was significantly higher among MSSA-infected patients treated with vancomycin than among those treated with cloxacillin (47% vs. none; P<.01). Multivariate analysis (stepwise logistic regression method) showed a relationship between mortality and the following variables: septic shock (odds ratio [OR], 61), vancomycin treatment (OR, 14), and respiratory distress (OR, 8).