MRSA: Community and Hospital Transmission Common, Study Shows

Lara C. Pullen, PhD

October 25, 2017

New data suggest that a ward-based approach to methicillin-resistant Staphylococcus aureus (MRSA) infection control is inadequate to address patient-centric transmission in hospitals and communities.

When Francesc Coll, PhD, research fellow at the London School of Hygiene and Tropical Medicine in the United Kingdom, and colleagues analyzed genomic clusters of MRSA, they found three strong epidemiological links: shared post codes, shared general practitioner practice, and shared ward contacts other than the accident and emergency department.

"Our findings have important implications for infection control policy and practice," Dr Coll and colleagues write. "MRSA transmission in our study population was not attributable to large nosocomial outbreaks but resulted from the cumulative effect of numerous clinically unrecognized episodes. We detected 173 separate genetic clusters that mapped to numerous different locations over the course of 12 months, which is indicative of repeated lapses in infection control." They published their results in the October 25 issue of Science Translational Medicine.

The investigators performed their epidemiological study during a 1-year period in the east of England, analyzing samples from three hospitals and 75 general practitioner practices. Patients had a mean age of 68 years.

The researchers sequenced the MRSA isolates and identified at least one MRSA isolate from 1465 individuals for a total of 2282 MRSA isolates. Using genome comparisons to assign the isolates to clusters, they were able to assign 40.8% of the patients to 173 transmission clusters containing between 2 and 44 cases.

When they paired each case with the individual whose MRSA isolate was the closest genetic match, they found a direct relationship between bacterial relatedness and strength of epidemiological contact.

"By including patient epidemiological information, we found that residential postcodes and [general pratitioner] registration information were strong epidemiological markers of MRSA transmission," they write. "Sharing the same postcode or [general practitioner] practice by two or more MRSA-positive patients often indicated an outbreak, some of which spanned several months."

The researchers did not track longitudinal or discharge MRSA screening in hospitals, nor did they screen environmental reservoirs and healthcare workers.

Most infectious control experts believe there are two types of MRSA lineages: one that adapts to persist and spread in hospitals and another that successfully competes with other S aureus lineages to spread throughout the community. The new data from Dr Coll and colleagues indicate that both community-associated and hospital-associated MRSA lineages are capable of transmission throughout the community.

"[W]e provide evidence for the value of integrated epidemiological and genomic surveillance of a population that accesses the same health care referral network in the East of England," they write. Such research may reveal, as theirs has, that current infection control policy and practice may be inappropriate.

One author is on the advisory board for Discuva Ltd. Two others are paid consultants for Specific Technologies.

Sci Transl Med. 2017:9:eaak9745. Abstract

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