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An outbreak of Acinetobacter baumannii: the importance of cross-transmission
E M D'Agata1, V Thayer, W Schaffner
1Department of Medicine, Vanderbilt University School of Medicine, Nashville, Tennessee, USA.
Objective:
To investigate an outbreak of nosocomial infections due to multidrug-resistant (MDR) Acinetobacter baumannii and to analyze the contribution of cross-transmission in the rise in infection rates.
Design:
Epidemiological investigation; molecular typing using pulsed-field gel electrophoresis (PFGE); matched case-control study to identify risk factors for infection.
Setting:
A 34-bed surgical intensive care unit at a tertiary-care hospital.
Patients:
Eighteen patients who developed MDRA baumannii nosocomial infection were matched to 36 patients who were admitted to the same surgical intensive care unit (SICU) room and did not develop an infection during the outbreak period.
Results:
Prior to the outbreak, the baseline attack rate of MDR A baumannii nosocomial infections was 3 per 100 patients per month. From February 1 through March 22, 1998, the attack rate rose to 16 per 100 patients per month, with a total of 18 infections. All isolates had indistinguishable PFGE patterns. Seventy environmental cultures were negative for MDR A baumannii. Following intense infection control education, the attack rate decreased to 4 per 100 patients per month. By conditional logistic regression, cases were exposed to a significantly higher number of patients with MDR A baumannii infections compared to controls (odds ratio, 1.1; 95% confidence interval, 1.01-1.2; P=.02), even after adjusting for length of SICU admission and exposure to antibiotics and invasive devices.
Conclusion:
Cross-transmission between patients contributed to the rise in rates of MDRA baumannii infections. A common environmental source was not detected.
Insights
Patient cross-transmission significantly increased multidrug-resistant Acinetobacter baumannii infections in a surgical ICU. Enhanced infection control measures successfully reduced the outbreak rates.
Area of Science:
- Infectious Disease Epidemiology
- Hospital-Acquired Infections
- Antimicrobial Resistance
Background:
- Nosocomial infections pose a significant threat in healthcare settings.
- Multidrug-resistant Acinetobacter baumannii (MDRA) is a challenging pathogen in intensive care units.
- Understanding transmission dynamics is crucial for controlling outbreaks.
Purpose of the Study:
- To investigate an outbreak of nosocomial infections caused by multidrug-resistant Acinetobacter baumannii (MDRA).
- To determine the role of patient cross-transmission in the increased infection rates.
- To identify risk factors associated with MDRA infection during the outbreak.
Main Methods:
- Epidemiological investigation and molecular typing (PFGE) of MDRA isolates.
- Matched case-control study comparing infected patients with uninfected controls.
- Analysis of risk factors including patient exposure, length of stay, and device use.
Main Results:
- Infection rates increased from 3 to 16 cases per 100 patients per month during the outbreak.
- All MDRA isolates exhibited indistinguishable PFGE patterns, suggesting a common source or strain.
- Exposure to a higher number of patients with MDRA infections was a significant risk factor (OR, 1.1; P=.02).
Conclusions:
- Patient-to-patient cross-transmission was a major contributor to the rise in MDRA infections.
- No common environmental source for the outbreak was identified.
- Targeted infection control interventions and education led to a decrease in infection rates.
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