Increase in methicillin-resistant Staphylococcus aureus acquisition rate and change in pathogen pattern associated with an outbreak of severe acute respiratory syndrome

Abstract

Background: An outbreak of severe acute respiratory syndrome (SARS) occurred in our 22-bed intensive care unit (ICU; Prince of Wales Hospital, Hong Kong, HKSAR, China) from 12 March to 31 May 2003, when only patients with SARS were admitted. This period was characterized by the upgrading of infection control precautions, which included the wearing of gloves and gowns all the time, an extensive use of steroids, and a change in antibiotic prescribing practices. The pattern of endemic pathogenic organisms, the rates of acquisition of methicillin-resistant Staphylococcus aureus (MRSA), and the rates of ventilator-associated pneumonia (VAP) were compared with those of the pre-SARS and post-SARS periods.

Methods: Data on pathogenic isolates were obtained from the microbiology department (Prince of Wales Hospital). Data on MRSA acquisition and VAP rates were collected prospectively. MRSA screening was performed for all ICU patients. A case of MRSA carriage was defined as an instance in which MRSA was recovered from any site in a patient, and cases were classified as imported or ICU-acquired if the first MRSA isolate was recovered within 72 h of ICU admission or after 72 h in the ICU, respectively.

Results: During the SARS period in the ICU, there was an increase in the rate of isolation of MRSA and Stenotrophomonas and Candida species but a disappearance of Pseudomonas and Klebsiella species. The MRSA acquisition rate was also increased: it was 3.53% (3.53 cases per 100 admissions) during the pre-SARS period, 25.30% during the SARS period, and 2.21% during the post-SARS period (P<.001). The VAP rate was high, at 36.5 episodes per 1000 ventilator-days, and 47% of episodes were caused by MRSA.

Conclusions: A SARS outbreak in the ICU led to changes in the pathogen pattern and the MRSA acquisition rate. The data suggest that MRSA cross-transmission may be increased if gloves and gowns are worn all the time.

Figure 1

Methicillin-resistant Staphylococcus aureus (MRSA) importation rates and acquisition rates (calculated as cases per 100 admissions) associated with an outbreak of severe acute respiratory syndrome in an intensive care unit (ICU) from January 2001 through December 2003.

Table 1

Rates of importation and ICU acquisition of methicillin-resistant Staphylococcus aureus (MRSA) before, during, and after an outbreak of severe acute respiratory syndrome (SARS) in a Hong Kong hospital.

Figure 2

Rate of isolation of pathogens from culture before, during, and after an outbreak of severe acute respiratory syndrome (SARS) in an intensive care unit (ICU). *Significantly different during the SARS period, compared with the pre-and post-SARS periods.

Table 2

The body sites from which the selected main pathogens were cultured.

Figure 3

Antibiotic use rates (calculated as defined daily doses [DDDs] per 1000 patient-days) of the selected commonly used antibiotics in the intensive care unit (ICU) before, during, and after an outbreak of severe acute respiratory syndrome (SARS). *Significantly increased during the SARS period, compared with the pre- and post-SARS periods. The ampicillin group includes amoxicillin/clavulanate, ampicillin/sulbactam, and ampicillin. The antipseudomonal penicillin group includes piperacillin and piperacillin/tazobactam. The third-generation cephalosporin group includes ceftazidime, cefotaxime, ceftriazone, and cefoperazone/sulbactam. The carbapenam group includes imipenam/cilastatin and meropenam. The quinolone group includes ciprofloxacin and levofloxacin. The aminoglycoside group includes netilmicin, amikan, and gentamycin.