MRSA

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Question Received:

  1. While nursing I came into contact with a patient with MRSA. I am concerned that I may have become contaminated and also contaminated my home, even though I have tested negative for MRSA. I am now pregnant. How long can MRSA persist in the environment?

Response:

While nursing I came into contact with a patient with MRSA. I am concerned that I may have become contaminated and also contaminated my home, even though I have tested negative for MRSA. I am now pregnant. How long can MRSA persist in the environment?

27th March 2001

According to my colleague who is a microbiologist and the infection control team at our hospital, survival of Methicillin-resistant Staphylococcus aureus (MRSA) depends upon the size of the population present - the larger the number of bacteria present the greater the potential for survival - and the availability of a suitable medium to support survival.

Given that there are a number of strains of MRSA it is only possible to give a general guide. It appears the organism may survive, in a domestic environment, for anything from 3-4 days to several months. Skin scales which have been shed and lodge in floor coverings may favour survival for a period of 6 months or more.

At this point I feel it is important to stress that if an individual's external body defences are intact the risk of MRSA actually being responsible for causing any infection must be very small. Added to this, even during MRSA outbreaks within hospitals the yield from the environment is apparently small. Cultures taken from a hospital environment have generally proved negative during outbreaks except in burns units (Crossley et al, 1979). When an outbreak of MRSA occurs, it is not common for healthcare staff to become infected. Rather they more commonly become colonised in the nose. The likelihood of staff colonisation is low and appears to be related to the amount of patient contact (Mackenzie and Edwards, 1997).

Teare and Barrett (1997) make the following points: there are other staphylococci, resistant to antimicrobial agents, implicated in a variety of diseases and spread within hospitals. Yet there is no suggestion that carriers should be found and treated. Screening is unhelpful and has not resulted in a decline in MRSA infection. Attempts made towards eradicating the organism in asymptomatic people is not really justified and that - harbouring the organism, by staff, is compatible with continuing health.

Your negative test result for MRSA is reassuring in that it suggests that you are not a carrier of MRSA now and may never have been. You may wish to repeat the tests again at some point to put your mind completely at rest. Tests for nasal carriage are probably the most reliable, but should be backed up with tests of other regions of the body. It is important that you feel calm and relaxed during pregnancy, so negative results to these tests will help you in this. If you are indeed not carrying MRSA, then it becomes most unlikely that your home has become contaminated with this bacterium, and again you should not worry about this possibility. This is not to minimise the risks attached to MRSA, rather to take account of your own situation and to ensure that you do not worry unnecessarily during your pregnancy. The following observations from the research into this topic are for information only and are not directly relevant to your own circumstances.

MRSA can be persistent both free in the environment and when colonizing asymptomatic carriers. If the host human becomes vulnerable, MRSA can cause a serious infection. The survival times of five strains of MRSA bacteria away from the body were determined by Wagenvoort, Sluijsmans, and Penders (2000). All strains survived for at least 6 months, and some survived for several months longer. MRSA persisted in the oral cavities of children for more than five years with the potential to cause nosocomial infections (Suzuki et al, 1997). Sanford et al (1994) found in a study of re-admitted MRSA-carrying patients that the majority carried MRSA for more than three years. However, in a study of patients in The Netherlands, those who left hospital colonized by MRSA generally became clear of the organism during the subsequent year provided that they did not have predisposing open lesions such as ulcers or orthopaedic bone fixations (Zetsma, Spanjaard, and Dankert, 1993). In this study there was no evidence of transmission of MRSA to healthy individuals. In another study by Hollis et al (1995), transmission of MRSA was confirmed within a family. The study by Mitsuda et al (1996) found Staphylococcus aureus carriage among pregnant women and newborn infants, including MRSA, and confirmed the possibility of mother-to-infant infection. Healthcare providers may become transient or persistent MRSA carriers whilst working in hospitals in which MRSA is endemic (Mitsuda et al, 1999). They may then become a source of infection for patients as well as their own families. At some hospitals, patients colonised with MRSA are considered to become lifelong carriers and potentially contagious when readmitted. However, the study by Beaujean et al (1999) found that open skin lesions were the main risk factor for prolonged colonization, and in their absence prolonged MRSA colonization did not occur.

Intranasal mupirocin ointment is effective in the control of MRSA (Hill, Duckworth, and Casewell, 1988; Gordon, 1993; Bertino, 1997; Hitomi et al, 2000). Mupirocin is a naturally occurring antibiotic produced by fermentation of Pseudomonas fluorescens. It inhibits bacterial protein synthesis by binding reversibly and specifically to isoleucyl-tRNA synthetase. Mupirocin is highly active against Staphylococcus aureus and other staphylococci and streptococci. However, MRSA strains resistant to mupirocin have emerged in many hospitals in the UK, so the treatment must be used judiciously (Cookson, 1995).

Although mupirocin has been tested by the manufacturers on rats and rabbits at high levels without harmful effects on fertility or prenatal development, there have been no controlled studies to determine safety during pregnancy in humans.

Hopefully, you will find the information we have provided useful and reassuring. It is important not to exaggerate the implications from nursing anyone with an infectious disease, or to become casual and lax. My understanding is that providing infection control guidelines are followed and staff realise the importance of their skin and mucus membranes remaining intact to provide an effective defence against microbial invasion, then the problem becomes more academic rater than practical.

References

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