Empyema is associated with a wide range of complication and mortality. It is defined by either a positive pleural fluid culture or grossly pus appearance. However, little is known about the differences in aetiology and outcome between culture-positive empyema (CPE) and culture-negative empyema (CNE). The aim of the current study is to look at the local prevalence of CNE, and compare the clinical outcome between CPE and CNE.

Pneumonia is a common disease and it ranked second as the leading cause of death in Hong Kong in 2016. Among patients suffering from acute pneumonia, up to 57% of them would develop parapneumonic effusion. Without proper treatment, parapneumonic effusion would progress into empyema, which is a clinical emergency. Empyema leads to a longer length of hospital stay, a higher rate of complication and mortality than uncomplicated parapneumonic effusion.

The mainstay of treatment for empyema is antibiotics and drainage. Therefore, identification of causative microorganism is important in guiding the choice of antibiotics. The common bacterial culprits, for community acquired and hospital acquired, were identified by various local and international studies. However, the aetiological agents were still unknown in up to 40% of cases. In addition, the clinical outcomes between culture negative empyema (CNE) and culture positive empyema (CPE) are largely unknown. Data from one Taiwanese study suggested that patients with CPE had a higher in-hospital mortality than those with CNE. However, the primary objective of this study was not putting on the importance of CNE. Therefore, data on outcome of CNE patients remain largely uncertain, either worldwide and local population.

The aim of the current study is to look at the local prevalence of CNE, and compare the clinical outcome between CPE and CNE. Through more understanding of CNE, the clinical management of this patient group may be altered and a better patient outcome is anticipated.

Inclusion Criteria:

i. All patients hospitalized for empyema, defined by the presence of purulent pleural fluid or positive culture result from pleural fluid ii. Age greater than 18 years old

Exclusion Criteria:

i. Inappropriate diagnosis of empyema after evaluation ii. Tuberculous pleuritis, defined by presence of Mycobacterium tuberculosis culture from pleural fluid or granulomatous inflammation on pleural biopsy histology

A. By using the International Classification of Diseases, Tenth Revision, Clinical Modification code 510.0 or 510.9, all primary hospital discharge diagnosis of empyema during a 5 year period, between 1st January 2013 to 31st December 2018

all IPD that underlie results in a publication

Starting 6 months after publication

upon individual approach for metaanalysis or related study