Placement of Patients in a Hospital Can Determine Course of MRSA Infection


One of the most challenging aspects of infection prevention and control is identifying the source of an outbreak or the route disease transmission is taking. Epidemiology is a critical aspect of infection prevention efforts, especially in the face of such prolific organisms as methicillin-resistant Staphylococcus aureus(MRSA). 

MRSA is one of the most common resistant organisms we face in healthcare infection prevention. The US Centers for Disease Control and Prevention (CD) estimates that in the United States, there are nearly 120,000 Staphylococcus aureus-related bloodstream infections each year and roughly 19,000 deaths as a result. The CDC also reports that 5% of patients in U.S. hospitals carry MRSA in their nose and on their skin.  

While MRSA transmission is relatively easy to control through detection, environmental disinfection, and isolation precautions, it continues to cause a considerable burden on patients and the US healthcare system. Understanding how the microorganisms transmit through healthcare facilities and the risk factors involved is vital to breaking the chain of transmission. Researchers in Canadaare working to combat this very issue, noting that in 2010, 4.2% of Canadian hospitalized patients became infected or colonized with MRSA. The burden of this bug is so significant, it costs an annual $28 million in the United States alone. 

By employing a case-control study using secondary data through tertiary health care patients, they assessed patients who were infected or colonized compared to matched controls. Analyzing the role of age, sex, and campus over the course of a year, the research team sought to understand those risk factors so that they could work to create more effective prevention and control strategies. 

A 1,118-bed tertiary care hospital in Ottawa was the setting for this 3-campus study. Cases were patients who tested positive for MRSA (targeted or screening) and cases were pulled from eligible patients who were screened for MRSA during the course of hospitalization and were negative throughout the study period. They were paired through roommates, rooms, and attending physicians in chronological order. The researchers noted that they “evaluated the ‘connectedness’ of groups of patients and places by counting groups of people and places with at least 1 link between them (components), as well as by the proportion of links existing in a component out of all those that could exist (density). Finally, we examined the immediate influence or importance of each person and place by the number of direct connections each one had (degree).”

Over 49,000 patients were admitted during this time and 746 were identified as having MRSA, with 547 meeting the definition of the case. There wasn’t much of a difference between cases and controls in terms of comorbidity, length of stay, mortality, number of roommates, rooms, and healthcare providers. To communicate their results, the team created a time animation of the transmission network, which showed potential source patients linked to two rooms and several roommates, “after which cases connected to those same rooms proliferated.”Researchers were able to study transmission prior to and during MRSA outbreaks at three of the campuses. Those cases at one campus were more connected, which researchers estimated to be a result of an increase in rooms and roommates prior to their MRSA infection. Overall, they found that utilizing network animation over time, transmission routes could be more easily identified through the network. This approach sheds light on potential avenues to employees when not only responding to outbreaks, but working to be more proactive and specific in infection prevention measures. 

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