Preventing the spread of MRSA

“The lack of evidence of an effect associated with specific measures should not be mistaken for evidence of lack of effect” is one of the conclusions that Cooper et al (p 533) come to after a systematic review of the literature about methicillin resistant Staphylococcus aureus (MRSA).¹ The infection control community has long realised that in the age of evidence based medicine and randomised controlled trials some, if not most, guidelines are based on shaky grounds. Is a method developed primarily for drug research and licensing appropriate for evaluating infection control procedures? Randomised controlled trials are useful for investigating a limited number of variables and when randomisation can be accomplished. Infection control measures are habitually complicated and depend on multiple factors. Therefore I still have some faith in the strength of common sense, microbiological experiments, and careful observation of success and failure when evaluating infection control measures.

The lack of evidence that this review finds should not be used to support arguments that efforts to control MRSA are costly and ineffective. This would be incorrect and harmful.

Despite the limitations of existing studies, Cooper et al found proof that concerted interventions, including isolation measures, can substantially reduce the transmission of MRSA. As someone working in a country that has a low prevalence of MRSA and uses the most intensive and comprehensive forms of infection control measures, I welcome the fact that the reviewers were not able to assess the relative contribution of individual infection control measures.² Those of us who apply the search and destroy principle know by experience that these measures work only when used in a concerted manner. Thus to single out one or a few measures, especially on the basis of limited evidence, risks potentially effective measures being neglected in future guidelines.

Unfortunately, much of the experience gained in Scandinavia and the Netherlands is published only as empirical evidence or does not meet the inclusion criteria for endemic and epidemic MRSA. None the less, the fact that these countries were and still are able to control the spread of MRSA transmission should not be ignored.

One crucial measure to control the transmission of MRSA, which is not evidence based and therefore not necessarily included in recent guidelines (for example, the United States guidelines), is the screening and decolonisation of healthcare workers.³ We have known for more than 50 years that nasal self inoculation of Staphylococcus aureus by hand to nose transfer happens subconsciously all the time. Not all carriers will shed MRSA into their environment, but this may easily change with the onset of, for example, a viral respiratory infection.⁴ Furthermore, numerous reports describe outbreaks related to colonised healthcare workers. Do we really need better studies to estimate the value of this measure, or can empirical data from the past 20 years combined with “old literature” about Staphylococcus aureus and common sense be enough to evaluate this measure?

Even though Cooper et al did their utmost to exclude bias while reviewing the studies, one form, “non-performance bias,” cannot be excluded from any study. This refers to failure to perform all that someone agreed to do to prevent hospital infection under pressures such as lack of money, scarcity of hospital staff, and overcrowding of hospitals. Another bias is intrinsic and is due to the transmission and control of MRSA and is influenced by many variables, including some that are indirectly linked to infection control, such as the presence and quality of isolation rooms.

The control of MRSA is and will continue to be of utmost importance to the infection control community. Half hearted practices and failure to follow guidance under pressure will in the long run fail and frustrate any infection control effort.

For now, we will have to use infection control guidelines based on the current knowledge and experience. The lack of evidence, as reported by Cooper et al, is not a convincing argument for changing successful infection control strategies such as the use of the search and destroy strategy. While waiting for hard evidence we should have faith that we are doing the right thing.