A longitudinal analysis of methicillin-resistant and sensitive Staphylococcus aureus incidence in respect to specimen source, patient location, and temperature variation

- The results indicate a gradual but steady increase in the incidence of methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-sensitive Staphylococcus aureus (MSSA) infections, with outpatient cases representing the majority of infections. The top three most common infections in order of prevalence were wound, respiratory tract, and urinary sources. The rate of infection was distributed equally between males and females.
- Although there was a slight increase in inpatient and nursing home MRSA cases, these cases consistently contributed to a smaller fraction of the total cases over the 5 years.
- If present, the cyclical nature of MRSA infections was directly related to the specimen source and patient location, with wound infections from outpatients more prevalent in warmer months, and respiratory infections among inpatients commonly observed during the colder months. This seasonal variation was absent among the nursing home population.
- The current report provides a longitudinal analysis of staphylococcal epidemiology, and in the process, identifies the staphylococcal seasonality to be multifactorial and to depend on various environmental factors, such as patient subpopulation and specimen source.

SummaryObjectiveSeasonal variations in temperature exert strong selective pressure on microorganism population dynamics and should be taken into account in epidemiological studies. The objective of the present study was to characterize the seasonal variation of staphylococcal infections in respect to patient location, specimen source, month of year, and temperature variation.MethodsA retrospective longitudinal time-series analysis of methicillin-resistant and methicillin-sensitive Staphylococcus aureus (MRSA and MSSA) was conducted in northeastern Ohio over a 5-year period. Multivariable time-series analyses were performed to detect the variations in the monthly incidence based on location of patients (inpatient, outpatient, and nursing homes), source of specimen (wound, respiratory tract, and urine), time of year (January-December), and temperature variation (average monthly over 5 years).ResultsThe results indicated a gradual increase in both MRSA and MSSA infections, with outpatient cases representing the majority of cases. If present, the seasonal nature of MRSA infections varied based on specimen source and patient location, with wound infections from outpatients more prevalent in warmer months, and respiratory infections among inpatients more prevalent during colder months.ConclusionsThe current report provides a longitudinal analysis of staphylococcal epidemiology, and in the process, identifies the seasonal nature of infections to be multifactorial, depending on such variables as specimen source and patient location. The seasonal nature of staphylococcal infections appears to be the product of a complex interaction among host, pathogen, and environment.