Aetiology of Adult Community-Acquired Lung Abscess in Hong Kong

Knowing the Pattern of pathogens in community-acquired lung abscess (CALA) is important in the choice of initial empiric antibiotics. Early studies established the anaerobes as the predominant pathogen, followed by aerobic streptococci and aerobic Gram-negative bacilli. However, recent reports indicated that Klebsiella pneumoniae and aerobic streptococci predominated.

We performed a retrospective study on CALA cases from all public hospitals in Hong Kong over a nine-year period. Only cases with uncontaminated specimens sent for bacterial culture were included. Cases caused by mycobacteria and fungi were excluded.

There were 606 eligible subjects-episodes. Mean age of subjects was 57.7 years and male to female ratio was 3.3:1. Two hundred and thirty-two subjects had at least one positive bacterial culture, with a total of 338 pathogens isolated. Anaerobes were the predominant pathogen group with 103 isolates (30.5% of total). This was followed by aerobic streptococci (90, 26.6%), aerobic Gram-negative bacilli (67, 19.8%), and Staphylococcus aureus (56, 16.6%). Isolation of Staphylococcus aureus was closely linked to intravenous drug abuse, while isolation of Klebsiella pneumoniae (28 cases) was related to extrapulmonary abscesses, particularly of the liver. There were 14 cases of Pseudomonas aeruginosa with underlying chronic lung disease and major organ failure being risk factors.

Anaerobes and aerobic streptococci appear to be the major pathogens for primary CALA. Secondary lung abscess caused by haematogenous spread is commonly attributable to Staphylococcus aureus or Klebsiella pneumoniae . Choice of empiric antibiotics should take these into consideration together with local patterns of antibiotic resistance.