Community-Acquired Acinetobacter baumannii Infections in Northern California

Acinetobacter baumannii is a gram-negative coccobacillus which has emerged as an important cause of healthcare associated infections, and wound infections in military veterans returning from Iraq and Afghanistan [1,2]. It may colonize tracheostomy sites, open wounds and environmental surfaces which serve as a nidus of spread via contaminated hands of healthcare personnel [3]. Hospital-acquired infections are characterized by high mortality rates and multi-drug resistance. Seasonal variation of A. baumannii infection rates has been noted with higher rates in the summer season [4].


Introduction
Acinetobacter baumannii is a gram-negative coccobacillus which has emerged as an important cause of healthcare associated infections, and wound infections in military veterans returning from Iraq and Afghanistan [1,2]. It may colonize tracheostomy sites, open wounds and environmental surfaces which serve as a nidus of spread via contaminated hands of healthcare personnel [3]. Hospital-acquired infections are characterized by high mortality rates and multi-drug resistance. Seasonal variation of A. baumannii infection rates has been noted with higher rates in the summer season [4].
Community-acquired A. baumannii infections have been recognized mainly in tropical and sub-tropical Asia-Pacific regions, such Taiwan, Hong Kong and Australia, and rarely in the United States [5]. Most reports describe patients with comorbidities, such as chronic obstructive pulmonary disease (COPD), renal failure and diabetes mellitus, although a few studies describe fulminant A. baumanii infections, such as pneumonia and severe sepsis, in otherwise healthy individuals. The mortality rate of community-acquired A. baumannii infections may be as high as 56%. Most cases have been caused by strains susceptible to third generation cephalosporins and carbapenems. In order to expand on the epidemiology of communityacquired A. baumannii infections in the United States, a detailed report is presented describing clinical characteristics and outcomes of cases seen at a medical center in Northern California.

Methods
A retrospective study was conducted of patients diagnosed with A. baumannii infection in Regional Medical Center of San Jose, CA, a 247-bed trauma medical center serving Santa Clara County, from January, 2009, until July 2011. Patients with A. baumannii infection seen in the emergency department wound care clinic or within 48 hours of admission to the hospital, without a history of hospitalization or residence in a long-term care facility in the preceding 30 days, were compared to hospitalized patients with healthcare-associated A. baumannii infections during the same period. Patients were deemed to have A. baumannii infections if they fulfilled infection criteria

Results
A total of 52 cases of A. baumannii infections were identified (Table 1). Of these, 11 (21%) were community-acquired, and consisted  of 5 wound infections (45%), 3 urinary tract infections (UTI, 27%), 2 pneumonias (18%), one of whom had bacteremia, and one bacteremia with shock (9%). Both cases associated with bacteremia developed septic shock and died. Healthcare-associated infections (41 cases) included a predominance of pneumonia (59%), and less commonly, wound infections (27%), UTI (12%) and bacteremia without death (2%). Community-acquired infections occurred in younger patients (average age 54 years compared to 70 years). All community-acquired cases were caused by fully susceptible A.baumannii strains, whereas 20% of hospital-acquired infections were associated with multi-drug resistance to penicillins, cephalosporins and carbapenems. Most cases (>75%) from both groups occurred during the months of December to May.

Comment
Community-acquired A. baumannii infections taken care of at a community-based medical center in Northern California, caused a variety of serious clinical syndromes, most commonly wound infections, but also UTI, pneumonia and septic shock (Table 1). In contrast, most healthcare-acquired cases were associated with pneumonia. Community-associated infections occurred in younger patients, and were lethal in both cases associated with bacteremia. Most patients in both groups had associated comorbidities such as COPD, diabetes mellitus and alcoholism. Unlike previously reported predominance in warmer months, most cases of both hospital and communityacquired A.baumannii infections were seen in late fall or winter months. Although multi-drug resistance was seen in 20% of healthcareassociated A. baumannii infections, all community-acquired infections were caused by fully susceptible strains. Local epidemiologic data, such as that found in this report, may be useful for the development of empiric treatment recommendations for A. baumannii infections by hospital-based antibiotic stewardship programs.