842. Community-Associated Methicillin-Resistant Staphylococcus aureus (CA-MRSA) Skin and Soft Tissue Infections (SSTI) in Chicago, 2005-8: High-Risk Clusters and Trends in Incidence
Session: Oral Abstract Session: MRSA - Epidemiological Trends
Saturday, October 22, 2011: 8:15 AM
Room: 157ABC

Background:   Few studies have examined trends in incidence of CA-MRSA SSTIs in a region.  We estimated CA-MRSA SSTI incidence and geographic and sociodemographic clustering.

Methods:  We identified 5447 adult and 1934 pediatric outpatient, emergency room, and inpatient CA-MRSA SSTIs from 2005-8 from Cook County Health and Hospitals System (CCHHS) and the University of Chicago Medical Center (UCMC).  The proportion of market share for SSTI inpatient discharge codes (CompData) for both centers by zip code and year was used to determine the at-risk population from annual zip code census populations.  Unadjusted CA-MRSA SSTI incidence per 100,000 population was calculated.  ArcGIS was used for geocoding.  Clusters were detected with Discrete Poisson Model of spatial scan statistic, SaTScan (v9.1.1).   Poisson regression was used to assess associations with year and zip code demographic characteristics.  The Wilcoxon rank sum test was used to compare demographics of cluster zip codes with others (Stata 11).

Results:  Patients were from 71% (132/187) of Cook County zip codes.  Mean incidence in 33 zip codes with adequate data for all 4 years rose from 402 to 522 in 2005-7 and stabilized at 521 in 2008.  The proportion of zip codes with incidence > 600 rose from 18% (7/38) in 2005, 25% (10/40) in 2006, 30% (13/44) in 2007, and to 34% (16/47) in 2008.  Higher zip code percentages of African Americans (AA) and individuals living in poverty (ILP) were associated in each year with higher incidence and higher percent Hispanic, with lower incidence.  Two clusters (p<0.001) were detected, representing 22% of cases—1 in 2006-7 and 1 in 2007-8 (Figure).  Zip codes in both clusters had higher median percent of AA (p=0.0003 and p=0.01) and ILP (p=0.003 and p=0.01) compared with all other zip codes.

For children, the number of high-incidence zip codes increased in 2005-7 and then declined; among adults, incidence increased steadily.

Conclusion:  The increase in CA-MRSA SSTI incidence in Cook County from 2005-7 may have plateaued in 2008 with possible divergence of adult and pediatric trends.  Geographic clusters were in areas with high poverty and AA population.  Understanding geographic clustering  may be critical for effective targeting of prevention efforts. 

Description: TotFinalMap_51311


Subject Category: N. Hospital-acquired and surgical infections, infection control, and health outcomes including general public health and health services research

Kyle J Popovich, MD1,2, Michael Z David, MD PhD3, Amanda E Grasso, MPH1, Robert S Daum, MD4, Bala Hota, MD, MPH1,2 and Diane S Lauderdale, PhD4, (1)Stroger Hospital of Cook County, Chicago, IL, (2)Rush University Medical Center, Chicago, IL, (3) University of Chicago Medical Center, Chicago, IL, (4)University of Chicago Medical Center, Chicago, IL


K. J. Popovich, None

M. Z. David, None

A. E. Grasso, None

R. S. Daum, None

B. Hota, None

D. S. Lauderdale, None

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