MRSA Superbug More Prevalent Than First Thought - New Survey

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Main Category: MRSA / Drug Resistance
Also Included In: Infectious Diseases / Bacteria / Viruses;  Public Health
Article Date: 25 Jun 2007 - 0:00 PDT

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A new survey of US healthcare facilities suggests that nearly 5 per cent of patients carry Methicillin-Resistant Staphylococcus aureus, the superbug known as MRSA, putting the national prevalence at between 8 and 11 times more than previous estimates.

According to its authors, the Association for Professionals in Infection Control and Epidemiology (APIC), the survey is the "largest and most comprehensive MRSA study of its kind," and the results showed that 46 out of every 1,000 patients "were either infected or colonized with MRSA".

The study has not yet appeared in a peer-reviewed journal, it is being presented at APIC's 34th Annual Conference in San Jose, California this week.

The researchers said that although the superbug is frequently detected in patients, the true burden of MRSA in the country's patient population is unknown. Apart from isolated reports from individual centres or hospital groups, national estimates are few and far between. And none until now has included both healthcare-associated-MRSA (HA-MRSA) and community acquired MRSA (CA-MRSA) and counts people who are colonized with the bug but don't have the disease.

Also, said the study authors, previous estimates have not taken into account the full range of different types of healthcare facilities, including for instance small community hospitals, nursing homes, and long term care facilities.

HA-MRSA is thought to be acquired in healthcare settings such as hospitals, while CA-MRSA is thought to be acquired in the community in places that contain environments favourable to the bug like locker rooms in schools, gyms and sports facilities.

HA-MRSA generally infects the blood, sites of surgical operations, or urinary tract. It also causes pneumonia.

CA-MRSA on the other hand usually causes skin and soft tissue infections. It is also more susceptible to antibiotics, particularly clindamycin and levofloxacin than HA-MRSA.

The survey included both APIC and non-APIC members who were asked to count all the patients known to be colonized or infected with MRSA as evidenced by medical records. Comprehensive data about the hospital setting and the type of infection or detection method were also collected.

Over 1,200 facilities provided data for the survey, which the researchers say is a statistically relevant sample because it represents about 21 per cent of all US healthcare facilities and 28 per cent of the average daily census. Their size ranged from 8 to over 1,500 beds and they were treating more than 185,000 patients between them (average of 69 each) when the survey was carried out.

The key findings included:

• The total number of patients with MRSA colonization/infection was 8,654.
• The overall MRSA rate (infection and colonization for both HA-MRSA and CA-MRSA) was 46.3 per 1,000 inpatients.
• The average infection only rate of MRSA (excluding colonization, as verified by culture positive testing) was 34 per 1,000 (range 16 to 48).

Detailed data was obtained on nearly 8,000 of the patients. This showed that:

• 54 per cent were male, 46 per cent were female.
• 67 per cent were on the medical service.
• 81 per cent were detected by clinical cultures and 19 per cent by active surveillance.
• 77 per cent were detected within 48 hours of admission and 23 per cent were detected after that period.
• 37 per cent had skin and soft tissue infections only (common CA-MRSA symptoms) and 63 per cent had infections at other sites (eg blood, pneumonia, urinary tract).
• Less than 30 per cent of isolated cultures were susceptible to clindamycin and less than 20 per cent were susceptible to levofloxacin.

The researchers said that the 48 hour after admission point is often used in the literature as an artificial cut-off to differentiate CA-MRSA from HA-MRSA, but they said this ignores the fact that many patients who could have become colonized at an earlier admission are re-admitted and may accidentally be counted as an CA-MRSA (caught by the under 48 hour cut off) when they should really be counted as an HA-MRSA case.

They said that including information about the site of the infection and susceptibility, gives a more reliable estimate and showed that the majority of infections were of the HA-MRSA and not the CA-MRSA type.

Click here for more information about MRSA from the US Centers for Disease Control and Prevention (CDC).

Click here for the Association for Professionals in Infection Control and Epidemiology (APIC).

Written by: Catharine Paddock
Writer: Medical News Today


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