To the best of our knowledge, the current study is the largest series of CAP-AB patients reported in the literature so far, and it is also unique in having a group of HAP-AB patients for comparison. CAP-AB was shown to be significantly different from HAP-AB in several aspects. First, CAP-AB patients were more likely to be ever-smokers and to have COPD, while other lung diseases or comorbid conditions, such as liver cirrhosis, diabetes mellitus, malignancy, and hematologic malignancy, were not predisposing factors. Second, the clinical presentation was more acute and fulminant with the conditions of more patients complicated by ARDS, and DIC. Third, CAP-AB patients were likely to have AB bacteremia on presentation and were less likely to have other concomitant organisms grown in culture from the same respiratory specimen. Fourth, antibiotic sensitivity was significantly different in the two groups, with HAP-AB isolates being more resistant than the CAP-AB isolates. Nevertheless, the appropriate empirical coverage of CAP-AB did not seem to alter the dismal prognosis. Finally, patients in the CAP-AB group had significantly higher mortality than patients in the HAP-AB group. Therefore, we propose that CAP-AB is a unique clinical entity, characterized by a high incidence of bacteremia, ARDS, DIC, and early deaths. this
Our study showed that CAP-AB usually occurs in elderly people with underlying COPD, and has a very acute and fulminant clinical course with very high mortality. Our findings confirm the observations made in previous uncontrolled case series. Anstey et al reported a series of 11 cases of blood culture-positive CAP-AB in Darwin in the Northern Territory of Australia during the 10-year period from March 1981 through February 1991. They found that the demographic risk factors included male gender, age > 45 years, and Aboriginal ethnic background. Multiple clinical risk factors, including cigarette smoking, alcoholism, chronic obstructive airway disease, and diabetes mellitus, were noted in all cases. A high mortality rate (64%) was observed in this cohort. A fatal outcome was strongly associated with inappropriate initial antibiotic therapy and shock at presentation. Chen et al did a retrospective review of 13 (9 men and 4 women; age range, 37 to 85 years) patients with CAP-AB. They found that conditions associated with CAP-AB included male gender, old age, alcoholism, malignancy, cerebrovascular disease, diabetes mellitus, renal disease, and liver cirrhosis.