The new superbug probably isn't leading to missed infections, at least in the United Kingdom, because hospitals that suspect a patient is infected with an MRSA nearly always use the antibiotic growth test in addition to PCR, Holmes says. (Patients with a confirmed infection then receive antibiotics that work on MRSAs.) However, many hospitals in continental Europe are moving toward using only PCR tests; this is a warning that those tests need to be modified to test for the new mecA gene, Holmes says.
The study also points to dairy cows as a possible reservoir for the bug, just as pigs seem to pass MRSA to humans in the Netherlands. The bug probably doesn't get to humans through the milk supply, because almost all milk in the United Kingdom and Denmark is pasteurized, a process that kills bacteria. But workers who come into contact with infected dairy cows could be carriers. Holmes's team reports "circumstantial evidence" for this, such as the fact that genetic subtypes of the human and cow samples from the same geographical areas were nearly identical. "The main worry would be that these cows represent a pool of the bacteria" that farm workers spread into the human population, Holmes says.