The good news is that your risk of getting a MRSA infection due to living with a MRSA carrier is not high. It’s not zero, either, but it’s not high.
The bad news is that we really don’t know how MRSA is transmitted within households, and thus we don’t know how to prevent it.
The best estimate I can find of co-colonization – not infection, just colonization – of MRSA within households is about 20% [1] . This number is an overestimate of transmission – 25% of co-carriers within households carry different strains of MRSA [2] , and thus couldn’t have transmitted it to each other. So your baseline risk of being colonized is about 15%. Whether other household members have an active infection or are merely colonized doesn’t seem to make much difference to the risk of transmission.
If you do become colonized, your risk of contracting an MRSA infection in the next four years is 15–20% [3] . So your overall risk of getting a MRSA infection is 15% (risk of colonization) x 15-20% (risk of infection if colonized) = 2–3%. By comparison, your yearly chance of needing medical care for an injury is about 12%.
Being colonized by MRSA is not a life sentence. The median duration of colonization is 41 weeks [4]. There’s a good chance that by this time next year, your roommate will not be colonized.
Risk factors for household transmission include the presence of small children [5] or companion animals [6] , intimate contact and sharing of lotions [7] , high housing density and frequent cleaning (and thus handling) of towels and linens [8] and material deprivation [9] . I’m sure there are more.
From Staphylococcus aureus infections: transmission within households and the community.
In other words, just about any plausible factor you can imagine has been implicated in MRSA transmission. That’s a problem, because it means that any simple intervention designed to reduce transmission is likely to fail – and has [10].
So, unfortunately, there are few specific steps you can take to reduce your risks. Your best bet is to minimize your exposure to the known risk factors and do all the things you should do to take care of your health anyway – wash your hands, eat well, get enough exercise and sleep, don’t smoke. Even if those things don’t prevent MRSA colonization, you still will be better off.
Footnotes
[1] Carriage of methicillin-resistant Staphylococcus aureus in home care settings: prevalence, duration, and transmission to household members.
[2] Staphylococcus aureus colonization among household contacts of patients with skin infections: risk factors, strain discordance, and complex ecology.
[3] https://www.ncbi.nlm.nih.gov/pmc…
[4] Natural history of colonization with methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococcus (VRE): a systematic r… – PubMed – NCBI
[5] Contamination of environmental surfaces with Staphylococcus aureus in households with children infected with methicillin-resistant S aureus.
[6] The shared microbiota of humans and companion animals as evaluated from Staphylococcus carriage sites.
[7] Risk factors for household transmission of community-associated methicillin-resistant Staphylococcus aureus.
[8] Persistent environmental contamination with USA300 methicillin-resistant Staphylococcus aureus and other pathogenic strain types in households with… – PubMed – NCBI
[9] Evidence for Community Transmission of Community-Associated but Not Health-Care-Associated Methicillin-Resistant Staphylococcus Aureus Strains Link… – PubMed – NCBI
[10] Staphylococcus aureus infections: transmission within households and the community.