MRSA: A Bit of Good News

February 24, 2009

Increasing microbial resistance to antibiotics is leading to an increase in MRSA infections in a variety of populations.

MRSA (methicillin resistant staphylococcus aureus) has become a scourge of public health. Increasing microbial resistance to antibiotics, as well as the ongoing rather casual use of these powerful agents, is leading to an increase in MRSA infections in a variety of populations. Some people becoming infected are in groups not previously considered at risk. This is a significant cause of both morbidity and mortality. Even young people are dying from MRSA infections.

However, in the article by Burton et al, some encouraging progress is seen. This report caught my eye as I used to see patients in a neurology/neurosurgery ICU, and MRSA was an ever-present problem. The authors report on trends in central line infections in ICUs, which are part of a voluntary monitoring coalition. They looked at data from 1997 to 2007 in a CDC database. While only 62 hospitals participated in 1970, by 2004 nearly 300 hospitals in 37 states were submitting data. Data were broken out by type of ICU, academic affiliation, and other factors.

Results

Overall, infections increased from 1997 to 2001, but decreased thereafter. A total of 33,587 infections were identified, of which 7.4% were MRSA and 4.7% were Staph infections sensitive to methicillin. The percentage of central line infections due to MRSA increased over the monitoring period. The bigger news, however, is the overall 49.6% decrease in MRSA infections in the period. This more than offset the increase in percentage of infections from MRSA. The biggest decrease in infections from 2001-2007, 69.2%, was seen in surgical ICUs. That is a decline of almost 3/4. These decreases mirror an overall decrease in central line infections over the period, and this may be responsible for some of the improvement in MRSA incidence. The one exception to the trend in MRSA infections was pediatric ICUs, but there was at least no increase seen over the monitoring period.

A variety of important limitations are highlighted. The specific contributors (prevention guidelines, central line insertion protocols, hand hygiene, etc) to the decrease are unknown. Also, many ICUs do not report infections to the database the authors studies, and the data do not cover infections outside the ICU or the hospital. The specific ICUs reporting changed over time, so the population studied was not homogeneous. And, possibly of most importance, the study looked only at Staphylococcus aureus and not other bacteria, which account for a large majority of central line infections (in particular coagulase negative Staph).

Also noted is the problem interpreting the oft-reported statistic of percentage of resistant infections, as this does not take into account the absolute incidence of MRSA infections, which may be decreasing. So, the reader is advised to take such percentage statistics with a grain of salt.

The interested reader is also referred to the editorial by Climo, which discussed this study in more detail.

This study is important. Whatever the underlying reasons, MRSA central line infections in adult ICUs have decreased a good deal. Perhaps measures such as better hand hygiene play a part. If so, we may see at least a leveling off of MRSA infections in other settings in future.