Study: Conditions in LA County Jail fostered spread of CA-MRSA

October 1, 2007

Modeling has shown that the large outbreak of community acquired methicillin-resistant S. Aureus (CA-MRSA) associated with the Los Angeles County Jail probably did not have its origin in that facility. That finding surprised the senior author of the study, Sally Blower, PhD.

Key Points

Los Angeles - Modeling has shown that a large outbreak of community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) associated with the Los Angeles County Jail probably did not have its origin in that facility.

That finding surprised the senior author of the study, Sally Blower, Ph.D. She and her associates at the Semel Institute for Neuroscience and Human Behavior at the University of California, Los Angeles, were intrigued by the outbreak of CA-MRSA, and thought the study might be a good example to illustrate the usefulness of mathematical models to the microbiology and medical communities.

"It is not some esoteric activity, but rather a good way to understand population dynamics and give you an idea of why a disease is spreading and what might be driving it," she tells Dermatology Times.

Jail conditions cited

The LA County Jail is the biggest in the country, with more than 165,000 inmates churning through over the course of a year; it houses some 20,000 at any one time. The study drew upon 8,448 confirmed cases of CA-MRSA reported at the jail between 2002 and 2005.

Using a variety of assumptions with regard to rates of colonization, active infection and other variables, Dr. Blower found the explanation that made the most sense was "that people were coming in to the jail colonized with MRSA, and, because of conditions at the facility, they were much more likely to go to infection rapidly."

It did not appear that inmates were being both colonized and proceeding to infection during a single period of incarceration.

Dr. Blower does concede the possibility that, because of the high rate of turnover among this population, "There might actually be more transmission going on in the jail than we could calculate with the data that we had."

There is no medical screening at discharge, and symptoms of a recent infection might not have become apparent prior to discharge.

The high rate of recidivism opens the possibility that some diagnoses of disease may have been the product of an infection during an earlier stay at county facilities, Dr. Blower says. She says an epidemiology study of genetic sequences of individual infections would be the only way to tell for sure.

The incarcerated population is at increased risk for a number of infectious diseases, which has prompted some public health experts to see the location as an excellent site for medical and educational interventions.

While Dr. Blower is sympathetic to the idea, the reality is that limited resources and the sheer volume of inmates makes that almost impossible.

"Logistically, they book hundreds of people a day at the jail. ... Each gets a cursory physical examination," she says. "Checking hundreds of people a day for MRSA is just not possible.

"At the beginning of the outbreak, jail officials thought that inmates were suffering from spider bites. So, people have to be aware of MRSA."

Dr. Blower says providing educational materials for both staff and inmates is a necessary and reasonable first step.

Other realities of the facility are that most inmates are not like socialite Paris Hilton, recently jailed on a probation violation after pleading no contest to alcohol-related reckless driving. The homeless are disproportionately represented among the incarcerated, and they often suffer from poor nutrition and hygiene, which contributes to the acquisition and emergence of CA-MRSA.

Inmates can take at most three showers a week. They have one change of clothes.

"So if they have a shower and put on their dirty clothes, they're going to get it," Dr. Blower says. "They have wounds on their skin. So colonization can quickly turn into infection. It is not that they are genetically more susceptible to infection."