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Epidemiological typing of methicillin-resistant Staphylococcus aureus outbreak isolates by pulsed-field gel
1Department of Clinical Pathology, Seoul National University Hospital, Korea. euichong@plaza.snu.ac.kr
Abstract:
Methicillin-resistant Staphylococcus aureus (MRSA) is one of the most common nosocomial pathogens. In April 1997, there were five MRSA-infected patients among 16 patients in the Neonatal Intensive Care Unit (NICU), Seoul National University Hospital, which is a tertiary-care hospital with 1,500 beds. The infections had spread from twin patients with MRSA who had transferred from Hospital C. MRSA was isolated from the axilla of 15 (94%) of the 16 patients, including the two patients with obvious infections. Three (19%) of 16 doctors and nine (30%) of 30 nurses had MRSA colonization of the anterior nares. Six different PFGE patterns (A through F) were identified in the 53 isolates of MRSA tested. Twelve of 13 isolates from infected sites of five patients showed pattern F. Three MRSA strains obtained from hospital C showed closely or possibly related pattern F. MRSA of type F was isolated from three of 16 patients' axilla, and one of 3 doctors' and three of 30 nurses' nasal swabs. The antibiogram code for 12 of 13 MRSA isolates from five infected patients was 66,754. PFGE patterns of these isolates were either F, F1, F2 or Fa. Only one of three strains isolated from clinical specimens of patients in Hospital C showed the antibiogram code 66754, although they were all PFGE types F1 and Fa. In conclusion, the presumptive sources of the outbreak of MRSA infection in NICU were the twin patients transferred from hospital C. Antibiogram correlated reasonably well to the PFGE type. An effective notification system is needed when a MRSA-infected patient is transferred to another hospital to control the spread of the infection.
Insights
Methicillin-resistant Staphylococcus aureus (MRSA) outbreaks in NICUs can spread rapidly. Transferring infected patients without proper notification facilitated MRSA transmission, highlighting the need for improved hospital communication to prevent future infections.
Area of Science:
- Infectious Diseases
- Hospital Epidemiology
- Microbiology
Background:
- Methicillin-resistant Staphylococcus aureus (MRSA) is a significant cause of hospital-acquired infections, particularly in vulnerable populations like neonatal intensive care unit (NICU) patients.
- A 1997 MRSA outbreak in a Seoul hospital's NICU involved a high proportion of patients and healthcare workers.
Purpose of the Study:
- To investigate the source and transmission dynamics of an MRSA outbreak in a tertiary-care hospital's NICU.
- To determine the molecular relatedness of MRSA strains involved in the outbreak.
- To assess the role of patient transfer in the spread of MRSA.
Main Methods:
- Pulsed-field gel electrophoresis (PFGE) was used to analyze the genetic profiles of 53 MRSA isolates.
- Antibiogram analysis was performed on MRSA isolates to compare resistance patterns.
- Epidemiological data, including patient transfers and healthcare worker colonization, were collected and analyzed.
Main Results:
- MRSA was isolated from 94% of NICU patients and a significant percentage of doctors and nurses, indicating widespread colonization and infection.
- PFGE identified six distinct MRSA patterns (A-F), with pattern F predominating in infected patients and healthcare workers.
- MRSA strains from a transferring hospital (Hospital C) showed genetic relatedness to the outbreak strains, suggesting a common source.
Conclusions:
- The outbreak was likely initiated by twin patients transferred from Hospital C, leading to MRSA spread within the NICU.
- Antibiogram results correlated well with PFGE typing, aiding in strain identification.
- Effective inter-hospital communication and notification systems are crucial for controlling MRSA transmission during patient transfers.