MRSA Entering US Hospitals Via Outpatients Is On The Increase

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Main Category: MRSA / Drug Resistance
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Article Date: 25 Nov 2009 - 2:00 PST

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A new study suggests that community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) is on the rise in US hospitals, and is adding to rather than replacing the type of MRSA that arises within hospitals, the hospital-associated MRSA (HA-MRSA); the study authors also found that the entry route for CA-MRSA is via outpatients who pick up the infection in places like gyms, schools and other public places.

The study is the work of Ramanan Laxminarayan, a senior fellow with the Washington DC think-tank, Resources for the Future, and colleagues from Princeton University and the University of Florida, and is available to read online in the December issue of the journal Emerging Infectious Diseases, published by the US Centers for Disease Control and Prevention (CDC).

Laxminarayan, who is is also affiliated to Princeton, is the Principal Investigator for Extending the Cure, a Resources for the Future project that examines policy solutions to the growing problem of antibiotic resistance. He told the media that:

"This emerging epidemic of community-associated MRSA strains appears to add to the already high MRSA burden in hospitals."

For the study, Laxminarayan and colleagues analyzed data from more than 300 microbiology labs used by hospitals all over the US and found that between 1999 and 2006 there was a seven-fold rise in the proportion of "community-associated" strains of MRSA in hospital outpatient units.

Since doctors and patients often move between inpatient and outpatient units, this rise in outpatient MRSA is a significant threat to patient safety in hospitals, suggested the researchers.

In summary, the results of the study showed that:

• From 1999 to 2006, the proportion of outpatients with staph who were infected with MRSA went up more than 90 per cent.


• This MRSA infected population now accounts for more than 50 per cent of all staph infections.


• It is likely that the rise in MRSA infections in almost entirely due to CA-MRSA.


• CA-MRSA rose from 3.6 per cent of all MRSA infections in 1999 to 28.2 per cent in 2006, a seven-fold increase.


• Similar increases in inpatients suggest that these strains are spreading rapidly in hospitals as well.

The researchers wrote that their findings suggest "outpatients have become a major reservoir for CA-MRSA", and contrary to other reports:

"Although CA-MRSA increases are associated with decreases in the frequency of HA-MRSA in hospitals, the decreases are only modest."

"This finding suggests that instead of replacing HA-MRSA in the hospital, CA-MRSA is adding to the overall presence of MRSA already found within the hospital population," they concluded.

The MRSA "superbug" is a deadly infection-causing bacteria that has become resistant to most common antibiotics; the community-associated strain now poses a far greater threat to health than ever before, and it is making its way into hospitals, said the authors.

MRSA attacks wounds and can trigger potentially fatal blood infections. Although CA-MRSA tends to be less virulent and is generally more treatable with antibiotics, it can still cause significant illness and deaths.

About 20,000 people in the US die every year from MRSA and there are more than 63,000 deaths each year linked to hospital acquired infections that are resistant to at least one antibiotic: this is more deaths than from AIDS, traffic accidents or flu.

The additional costs of treating antibiotic resistant staph range from 3,000 to more than 35,000 US dollars per case, reports Resources for the Future.

Eili Klein, lead author of the study, who is also a researcher at Resources for the Future, said:

"MRSA has generally been a significant problem only in hospitals."

"But the findings from this study suggest that there is a significant reservoir in the community as well," added Klein, who suggests this community reservoir leads to a dangerous spread of community-associated strains from outpatient units into hospitals.

The researchers propose that the most effective way to contain MRSA and other superbugs is through regional surveillance and infection control.

Klein said that the movement of CA-MRSA into hospitals also indicates an urgent need for rapid tests that differentiate the MRSA strains. Some MRSA strains, particularly the CA-MRSA ones are more susceptible to a wider range of cheaper antibiotics.

Investing in rapid testing of MRSA strains could help hospitals deal effectively with infections and reduce healthcare costs at the same time, while also helping to preserve national suppies of antibiotics, wrote the authors.

Extending the Cure is sponsored by the Robert Wood Johnson Foundation's Pioneer Portfolio, which supports new ideas for potential breakthroughs in health and health care.

"Community-associated Methicillin-Resistant Staphylococcus aureus in Outpatients, United States, 1999-2006."
Eili Klein, David L. Smith, and Ramanan Laxminarayan.
Emerging Infectious Diseases, Volume 15, Number 12, December 2009.
DOI: 10.3201/eid1512.081341

Source: Resources for the Future.

Written by: Catharine Paddock, PhD
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