Wednesday, October 17, 2007

Shock Media

"U.S. Deaths From Staph Surpass AIDS" says the AP. The first line of the article reads "About 18,700 people die in this country each year from drug-resistant staph infections, according to a federal study released Tuesday — more deaths than the United States sees from AIDS annually." This number comes from a CDC study on MRSA published in today's JAMA (JAMA 2007;298:1763-1771). Using the number of yearly AIDS deaths in the US cited in the Chronicle article, 17,000, then 1,700 more people die in the US every year from MRSA.

When reading the actual study, though, I get a slightly different feel.

Basically, the authors used a CDC surveillance procedure, monitoring 9 large urban areas for cases of MRSA, then obtaining medical records for each patient. Outcomes--death or discharge--were taken from the medical record.

Here's the thing, though: they never stated explicitly that the cause of death was MRSA. It's easy to imagine that a person with an invasive MRSA bacteremia would be critically ill, but how does one determine that the MRSA killed them, or the kidney failure which had them requiring dialysis which led to them getting MRSA in the first place? Or if someone is recovering from MRSA sepsis with DIC, then throws a massive pulmonary embolism and dies from being in the ICU for weeks, is the cause of death MRSA? It's also possible that a patient had a positive MRSA culture from a cellulitis, but died of something entirely unrelated, like an MI or CHF. They never stated that the cause of death was MRSA, only that these people a) had an invasive MRSA infection and b) died. If MRSA wasn't the direct cause of death in all of these patients, then the rate of death due to MRSA would be lower than they predicted.

Also, the only record of death came from the medical record for patients who died in the hospital. It's feasible to imagine that some patients died at home or in nursing homes from MRSA or its complications who weren't included. This would mean the rate could be higher than they estimated. Lastly, we're assuming that these 9 regions represent the US as a whole, but in reality bacterial populations vary by geographical regions. One of the sites studied, Baltimore, was left out of incidence calculations because it had much higher rates than the other 8 sites.

The point of the article was really to show that the rate of invasive MRSA infections is higher than previously supposed, and that a substantial amount of these infections came from the community. The majority of infections and deaths came from the healthcare-associated disease--patients who have been hospitalized recently, or have indwelling catheters and lines, or dialysis, or live in nursing homes, etc. Healthcare-associated infections also tended to be a more dangerous strain, USA100, with more multi-drug resistance, compared to community-acquired infections. Interestingly, although they gathered the data about the strain and presented it in the results section, they give it only a few sentences in the conclusion, as if the incidence data is so much more interesting.

Much of what got quoted in the Associated Press was an editorial about the study, also in today's JAMA (2007;298:1803-1804).
This is where the comparison to AIDS comes from and some of the other quotes used in various articles about this study today.

Naturally, MRSA is a huge problem. Isolates at one hospital I work at have developed alarming tolerance of vancomycin--not high enough to be considered vancomycin-resistant, but high enough that the concentration of vancomycin required for treatment is reaching dangerous levels. This hospital is considering a policy change to make linezolid the first choice antibiotic for MRSA. We're one step closer to VMRSA, a much scarier beast.

Most hospitals are not required to report MRSA rates (or any other drug-resistant bacteria) to authorities. Some hospitals have started nasal swab policies to identify MRSA carriers upon admission to isolate them sooner and prevent the spread to other patients. Hand washing policies are effective against the spread of nosocomial infections, but are sadly under-enforced.

I'm always a little amused by what the popular media will choose for their headlines, however. I guess they made their point: everyone knows about and fears AIDS, but few people know about MRSA.


enrico said...

Thanks for stealing my thunder. :P I just got the article tonight. Good observations.

Linezolid as the first-line agent? $$ CHA-CHING! $$ There are going to be some very sad pandas once they get their bills...

Does nobody even consider TMP/SMX or clindamycin anymore? Is this based on hard data or just "we don't want to screw with it, and the cheap stuff can't possible work...can it?"

Caroline said...

I had the same reaction. Leave it to CNN to think they are telling us something new and exciting.