nos-trum. pronunciation: \nos'-trum\. noun. Etymology: Latin, neuter of noster our, ours.
1. a medicine of secret composition recommended by its preparer but usually without scientific proof of its effectiveness.
2. a usually questionable remedy or scheme.
See here for more discussion.

Tuesday, April 20, 2010

Taking MRSA Out Of Hospitals, But Does Doing So Lower The Everyday Threat?

A recent 15-year study from France shows how an intensive effort can lower levels of disease-causing bacteria in hospitals.  But the impact on disease is not yet defined.

Common sense would argue that if you reduce the quantity of a harmful substance or organism, then less harm will be produced, but that's not always the case, and bacteria are a good example.

The study published Mar 22 in the Archives of Internal Medicine, examined efforts in Parisian hospitals since 1993 to reduce the incidence of methicillin-resistant staphylococcus aureus (the infamous MRSA), a drug-resistant disease-causing bacterium that has been implicated in outbreaks in the US and elsewhere.  Inflammatory articles have whipped up concerns to the point where schools have been closed for disinfection procedures--of dubious worth.  While sometimes lethal, MRSA is not anywhere near the upper ranks of public health threats.

By standard measures the effort--involving isolation, sanitation, and surveillance--significantly lowered the proportion of the resistant strain (MRSA) as compared to non-resistant, and lowered the "burden" (or amount) of MRSA in the facility.  Lastly the rate of MRSA cases also fell.

Sounds pretty straight forward, right?

There are several problems.

1.  There was no control group.  Not a killer objection, but when you look at some of the data, an alternative explanation is that MRSA levels fell naturally.  MRSA infections in ICU's in the US fell from 1997-2007, and the number of cases was independent of the proportion of MRSA present.

Squares are acute care hospitals, circles are long term care hospitals.

A control group would have showed whether the results were due to sanitary efforts or natural causes.  Note that the pre-study MRSA cases in acute hospitals was trending slightly downward, and in long term hospitals, by 2007, there was only a return to 1996 levels.

2.  Bacteria cause disease outbreaks not only because they are present in great numbers, but as a result of  a complex relationship to other pathogens present.  Even harmless bacteria can suppress or increase the activity of a disease-causing pathogen.  We don't know what was going on "behind-the-scenes" here, bacterially speaking.
3.  Even if the French effort caused a reduction in MRSA burden and disease, we don't know that this translates to any influence this program would have had on MRSA in the environment--like schools.  Hospitals disinfect day-in and day-out.  Schools who do a one-time cleaning will be re-colonized with MRSA in a few days (my guess).

For Onion Peelers, (math stuff)
The proportion (expressed as percentage) of MRSA among S aureus strains fell from 41.0% down to 26.6% overall, 45.3% to 24.2% in blood cultures. The incidence of MRSA cases fell from 0.86 down to 0.56 per 1000 hospital days. The MRSA burden decreased more markedly in intensive care units (–59%) than in surgical (–44%) and medical (–32%) wards.  All results were significant down to p=0.001 or less.

So, it's important not to take this research too far. A valuable study, it's enough to continue the program, while further research is done. But it's not time to take it to the bank (or to the school).

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