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Abstract:
Methicillin resistance in Staphylococcus aureus has been one of the major problems of gram positive infections in hospitals in the Zurich area. Up to 1971, about 20% of staphylococcal disease was caused by these peculiar organisms. Since 1972, however, a gradual decrease in the number of methicillin-resistant organisms has been observed, with an unprecedented low of 3% in 1975. The nearly 700 methicillin-resistant cultures that have isolated since 1965 exhibited, with rare exceptions, conventional group-II patterns of lysis in phage-typing and similar antibiotypes. It is suggested that all these isolates are derivatives of a strain which has long existed in the staphylococcal population. The reasons for the changes in the frequency of this strain as an agent causing staphylococcal disease are unclear. The use of penicillinase-resistant beta-lactam antibiotics in hospitals does not seem to play a major role in the distribution and spread or in the disappearance of this strain.
Insights
Methicillin-resistant Staphylococcus aureus (MRSA) infections decreased significantly in Zurich hospitals after 1971. This decline in MRSA, a common cause of gram-positive infections, occurred despite antibiotic use, suggesting other factors influenced its prevalence.
Area of Science:
- Medical Microbiology
- Infectious Diseases
- Hospital Epidemiology
Background:
- Methicillin resistance in Staphylococcus aureus (MRSA) posed a significant challenge for gram-positive infections in Zurich hospitals.
- MRSA accounted for approximately 20% of staphylococcal disease cases up to 1971.
Purpose of the Study:
- To investigate the trends and potential factors influencing the prevalence of methicillin-resistant Staphylococcus aureus in the Zurich hospital setting.
- To analyze the characteristics of isolated MRSA strains and their epidemiological patterns over time.
Main Methods:
- Retrospective analysis of Staphylococcus aureus cultures isolated from hospital patients between 1965 and 1975.
- Phage-typing and antibiotyping to characterize methicillin-resistant isolates.
- Correlation of MRSA prevalence with antibiotic usage patterns.
Main Results:
- A notable decrease in MRSA prevalence was observed starting in 1972, reaching a low of 3% by 1975.
- Nearly 700 MRSA cultures isolated since 1965 shared common phage-typing (group-II lysis) and antibiotyping patterns, suggesting a common strain origin.
- No significant correlation was found between the use of penicillinase-resistant beta-lactam antibiotics and the observed changes in MRSA frequency.
Conclusions:
- The observed fluctuations in MRSA prevalence in Zurich hospitals appear to be driven by factors other than the direct impact of penicillinase-resistant beta-lactam antibiotic usage.
- The findings suggest that a long-standing strain of MRSA may be responsible for infections, with its prevalence influenced by unelucidated epidemiological dynamics.