The Effect of Humidity on the Survival of MRSA on Hard Surfaces

Abstract

Methicillin resistant Staphylococcus aureus(MRSA) is an ongoing clinical problem world-wide and a recognised cause of nosocomial infection. In the UK it has been reported that approximately 100,000 patients acquire nosocomial infections per annum, of which 6000 die [1]. If MRSA survives for long periods in health-care environments, this may contribute to infection transmission from fomites. We evaluated the effect of humidity on the survival of MRSA on five different hard surfaces commonly found in health-care establishments. Adjusting the humidity of such environments may provide an inexpensive way of reducing MRSA prevalence. Tiles (1cm2) of five surface types including wood and Formica were inoculated with 5 105–5 106 ATCC EMRSA15 cells suspended in PBS with 1% BSA. EMRSA15 was chosen as it is the most common of two prevalent strains in UK hospitals. Multiple samples of each surface type were then incubated at 42%, 52% and 65% relative humidity (RH) at 23°C (room temperature). Cells from samples of each surface type were re-suspended; agar plates were inoculated and incubated overnight at 37°C and the number of colonies counted. Samples were taken every day for the first week, twice weekly for the following 2 weeks and once a week thereafter. Numbers of viable cells decreased over time from 5105–5106 at day one to below 2 104 by day 22. Minor differences in the rate of decline occurred with different humidities and surface types, generally showing a steep decline in numbers in the first 10 days and a slower decline thereafter. After 57 days numbers were less than 600 but some still persisted.

Longitudinal Study of the Contamination of Air and of Soil Surfaces in the Vicinity of Pig Barns by Livestock-Associated Methicillin-Resistant Staphylococcus aureus

“…It is likely that deposited LA-MRSA can survive for longer periods on soil surfaces. While there is no exact information about the survival time of MRSA on soil, it is known from laboratory experiments that human MRSA strains show high tenacity and can survive on hard surfaces for weeks (17). Therefore, we assume that deposited MRSA is able to accumulate on soil surfaces around the barns, provided that it is not washed away by rainfall.…”

Airborne Microorganisms Emitted from Wastewater Treatment Plant Treating Domestic Wastewater and Meat Processing Industry Wastes

“…De Luca et al [34] and Makison and Swan [42] reported the presence of coagulase negative staphylococci in different environments (in atmospheric air and on hard hospital surfaces) with low humidity. These bacteria may occur as agglomerations of cells, or may be rafted into the air on plant or animal fragments, on soil particles [40].…”

Effects of indoor environmental parameters related to building heating, ventilation, and air conditioning systems on patients' medical outcomes: A review of scientific research on hospital buildings

“…A strong correlation has been found between the transmission of viruses and absolute humidity, and viruses outbreak when the vapor content of the air decrease . Several controlled studies concluded that both RH and humidity ratio values influence the survival of viruses and bacteria …”