Antibiotic management of complicated parapneumonic effusion or empyema complicating community-acquired pneumonia in adults

Adults with community-acquired pneumonia (CAP) who develop a complicated pleural effusion (parapneumonic effusion) or empyema require:

• admission to hospital
• pleural fluid sampling and drainage
• intravenous antibiotics.

For the definitions of complicated parapneumonic effusion or empyema, and a summary of management, see Definitions and management of parapneumonic effusion and thoracic empyema.

In adults with complicated parapneumonic effusion or empyema complicating CAP, the most likely pathogens are:

• Streptococcus pneumoniae
• the Streptococcus anginosus (milleri) group (S. anginosus, S. constellatus, S. intermedius)
• anaerobes such as Bacteroides, Veillonella and Peptostreptococcus species.

Polymicrobial infection is common. Significant epidemiological variation exists worldwide – the S. anginosus (milleri) group are the most common pathogens in Europe, North America and Australia whereas Klebsiella species are the most common pathogen in South-East AsiaHassan, 2019. Staphylococci (predominantly Staphylococcus aureus and Staphylococcus lugdunensis) cause approximately 20% of culture-positive casesHassan, 2019Kanellakis, 2022. Streptococcus pyogenes (group A streptococcus) is an uncommon cause, but is important to consider because of the increasing incidence of invasive group A streptococcal (iGAS) infection. Atypical pathogens¹ (eg Legionella species, Chlamydophila [Chlamydia] pneumoniae, Mycoplasma pneumoniae) are unlikely to cause parapneumonic effusion or empyema.

Collect pleural fluid samples to analyse for:

• biochemistry (which may include pH, lactate dehydrogenase [LDH], protein and glucose)
• cytology
• culture.

Culturing pleural fluid in blood culture bottles, in addition to standard culture, can increase microbial yieldMenzies, 2011. Other investigations, such as nucleic acid amplification tests (NAAT) (eg polymerase chain reaction [PCR]), are sometimes performed on pleural fluid samples.

If available, use the results of microbiological investigations to guide antibiotic therapy, noting that these infections are typically polymicrobial.

Culture results are often negative because of preceding antimicrobial therapy for pneumonia, but also because it is possible that most organisms reside in pleural tissue rather than pleural fluidLee, 2018Psallidas, 2018. The role of routine pleural biopsy remains unclear outside of tuberculosisShaw, 2018. If microbiological results are not available or are negative, empirical therapy is stratified according to the severity of the underlying pneumonia (for assessment of pneumonia severity, see Severity assessment of CAP in adults). After assessing severity, see the antibiotic regimens for empyema and complicated parapneumonic effusion for low- to moderate-severity disease or high-severity disease.