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MRSA linked to lower incomes, larger households sizes
People with lower median household income were likely to have CA-MRSA on admission.
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ORLANDO, Fla. — Patients with lower median household incomes and larger household sizes showed greater prevalence of methicillin-resistant Staphylococcus aureus in a recent study of more than 25,000 people.
“Income and household size might warrant more attention than simply asking patients how much they make and who they live with,” said Marc-Oliver Wright, director of infection control at Evanston Northwestern Healthcare in Evanston, Illinois.
Wright presented study results at the 18th Annual Scientific Meeting of the Society for Healthcare Epidemiology of America, held here recently.
The study was conducted by the researchers at Evanston Northwestern Healthcare using admission information from three hospitals in the northern Chicago area. The researchers tested patients for Panton-Valentine leukocidin as a marker for potential virulence and prevalence of community-associated MRSA.
Cluster potential questioned
Wright cited a study conducted in Minnesota that compared community-associated -MRSA with health care-associated MRSA in relation to household income. In that study, CA-MRSA was associated with significantly lower median income than HA-MRSA. Both strains were associated with patients earning significantly less than the statewide per capita median income.
When looking for MRSA prevalence population clusters, however, patient proximity to the nearest hospital — a hospital which also may serve patients in public housing facilities — may confound true income-based risk factor identification.
In this study, plotting the addresses of patients with MRSA on area maps showed no strong population clusters, Wright said.
Large cohort studied
Patients (n=26,712) were identified through universal MRSA surveillance at three hospitals from April 19, 2007 to Dec. 31, 2007. Nares specimens were obtained from all patients at admission. Patients colonized with MRSA were identified by polymerase chain reaction, confirmation of culture growth, or history of MRSA within the past year. Three hundred and twenty-six patients had a history of prior clinical MRSA within the past 12 months and 1,038 patients (3.9%) were nasally colonized with MRSA.
In mid-April, the researchers added Panton-Valentine leukocidin testing as a marker for differentiating CA-MRSA from HA-MRSA. Panton-Valentine leukocidin data analysis revealed CA-MRSA prevalence was 5.1 patients per 1,000 admissions, representing approximately 13.1% of all MRSA strains in patients admitted during the study period.
Household size, median incomes, and demographics were collected through U.S. Census data. Known addresses for patients with MRSA were plotted on a map to determine potential MRSA cases clusters.
Risk factors
Several risk factors for MRSA colonization on admission were identified, including age, gender, emergent admission and transfer from a long-term care facility. Peptic ulcers and other comorbid conditions increased likelihood of nasal MRSA more than twofold.
Panton-Valentine leukocidin data also revealed a converse relationship to age and MRSA because MRSA risk usually increases gradually as patients’ ages increase. Using Panton-Valentine leukocidin testing for CA-MRSA, the reverse was true.
“The change is dramatic and flips backwards to higher risk for younger people,” Wright said. “Risk factors for Panton-Valentine leukocidin colonizations are different and this follows the emerging thought that not all bugs are created equal — even within MRSA.”
People with the lowest median household income according to census data also more commonly had CA-MRSA on admission.
“We found that if a person earned about $2,500 to $41,000 per year in household income in the northern part of Chicago, the risk for CA-MRSA colonization was greater than for a patient in the middle or upper class,” Wright said.
Patient outcomes
Patients admitted with MRSA were less likely be discharged to home after adjustments were made for long-term care facility transfer, age, direct admission to the ICU, length of stay, comorbidities and inpatient discharge within the past year.
Length of hospital stay increased slightly with MRSA positivity. Patients who were MRSA-positive stayed an average 5.34 days in the hospital and the average hospital stay for patients who did not have MRSA infection was 3.76 days.
Mortality among patients who had MRSA infections was three times higher after the researchers controlled for age, transfer from long-term care facilities and comorbidities.
Benefits worth expense
Active MRSA surveillance programs are costly. The cost for this study was estimated at $1 million. In a cost analysis of the first two years of the program, the researchers found a reduction in clinical MRSA cultures.
“Cost is certainly important when you are taking this as a business case to hospital administrators,” Wright said. “When we took a look at the number of clinical culture positives before and after implementation, there was a dramatic decline; so it was beneficial.” – by Kirsten H. Ellis
For more information:
- Naimi TS, LeDell KH, Como-Sabetti K, et al. Comparison of community- and health care-associated methicillin-resistant Staphylococcus aureus infection JAMA. 2003;290:2976-2984.
- Glenn KR, Craig A, Kainer MA. Thirty-day and 180-day case fatality rates among invasive methicillin-resistant Staphylococcus aureus patients (Tennessee, 2004-2007). #540. Presented at: The International Conference on Emerging Infectious Diseases 2008; March 16-19, 2008; Atlanta.