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MRSA: It’s Got Seasonality

 

 

 

# 5479

 


With our attentions diverted to the horrific tragedies in Japan, a number of important studies published over the past month have received less attention than they might otherwise.  

 

One such study that captured my attention appeared late last month in PloS One, that found a significant spike in MRSA infections reported by a Rhode Island Emergency room during warm weather months (3rd & 4th quarters of the year):

 

Seasonality of MRSA Infections

Mermel LA, Machan JT, Parenteau S (2011) Seasonality of MRSA Infections. PLoS ONE 6(3): e17925. doi:10.1371/journal.pone.0017925

Abstract

Using MRSA isolates submitted to our hospital microbiology laboratory January 2001–March 2010 and the number of our emergency department (ED) visits, quarterly community-associated (CA) and hospital-associated (HA) MRSA infections were modeled using Poisson regressions.

 

For pediatric patients, approximately 1.85x (95% CI 1.45x–2.36x, adj. p<0.0001) as many CA-MRSA infections per ED visit occurred in the second two quarters as occurred in the first two quarters.

 

For adult patients, 1.14x (95% CI 1.01x–1.29x, adj.p = 0.03) as many infections per ED visit occurred in the second two quarters as in the first two quarters.

 

Approximately 2.94x (95% CI 1.39x–6.21x, adj.p = 0.015) as many HA-MRSA infections per hospital admission occurred in the second two quarters as occurred in the first two quarters for pediatric patients.

 

No seasonal variation was observed among adult HA-MRSA infections per hospital admission. We demonstrated seasonality of MRSA infections and provide a summary table of similar observations in other studies.

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(Continue . . . )

 

 

By examining hospital and emergency room records at a Rhode Island hospital over a 10 year span, the authors demonstrated that pediatric patients experienced approximately 1.85 times as many community-associated (CA) MRSA infections and 2.94 as many hospital-associated (HA) MRSA infections in the second two quarters of the year as opposed to the first two quarters.

 

While a similar pattern was observed for adults, it was less pronounced, with 1.14 times as many CA-MRSA infections in the 3rd & 4th quarters, but no detectable increase in adult HA-MRSA infections.

 

As far as what might explain these seasonal differences, the authors point out that higher temperatures alone cannot not account for the increases.

 

Temperatures in the 2nd quarter of the year in Rhode Island are generally higher than in the 4th quarter. 

 

While there are many unanswered questions, the authors suggest that factors such as excessive hydration of the skin (sweating), summer insect bites, and warm, humid environments conducive to bacterial survival and spread may account for the rise.

 

The spike during the 4th quarter may be due to a delay between colonization and apparent infection, or may even be partially attributed to increases in respiratory infections during the fall months which may lead to greater S. aureus transmission.

 

While more research on this phenomenon is needed, for now this study continues to highlight the importance of personal hygiene; hand washing, showering, caring for breaks in the skin (cuts, scrapes, insect bites), and respiratory etiquette  - along with the disinfection of surfaces that are apt to be contaminated with Staphylococcus aureus.

 

See CDC webpage on Prevention of MRSA Infections.

 

Steps that are important year-round, but may take on even greater importance during the 3rd & 4th quarters of the year.

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MRSA
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