Stewardship / Resistance Scan for May 31, 2017

Livestock-associated MRSA
Antibiotic overuse in food animals

Study describes spread of livestock-associated MRSA in Denmark

Livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) appears to be spreading further into the community and healthcare settings in Denmark, researchers reported yesterday in Clinical Infectious Diseases.

In the study, researchers evaluated data on all Danish patients who were registered as having had an episode of MRSA bloodstream infection (BSI) or skin and soft tissue infection (SSTI) from 2010 through 2015. Using molecular sequencing tests, they set out to determine how many were caused by LA-MRSA clonal complex 398 (CC398), which has been causing an increasing number of human infections in Denmark and other European countries with industrial pig production. While SSTIs caused by LA-MRSA CC398 have been studied and are mainly associated with livestock workers, less is known about the strain's impact on BSIs.

The researchers also wanted to compare LA-MRSA CC398 BSI cases to SSTI cases caused by the strain and to BSI cases caused by other strains of MRSA, and to determine the phylogenetic relationship among LA-MRSA CC398 isolates from pigs and from human infections.

Overall, LA-MRSA CC398 accounted for 17 cases of BSI, 700 cases of SSTI, and 76 cases with other infections from 2010 through 2015. The number BSIs and SSTIs caused by the strain increased over the years and peaked in 2014, accounting for 16% (7 of 44) of BSIs and 21% (211 of 985) of SSTIs. Of the total LA-MRSA CC398 SSTIs, 32% (221 of 700) occurred in people with no livestock contact, while 59% (10 of 17) patients with LA-MRSA CC398 BSIs had no contact with livestock, although they tended to live in rural areas.

In addition, the researchers also found that LA-MRSA CC398 appears to be just as capable of causing serious illness in elderly and immunocompromised people, and that most of the BSI and SSTI isolates were closely related to Danish LA-MRSA CC398 isolates from Danish pigs, a finding that suggests zoonotic transmission from an expanding pig reservoir.

Even though Denmark has low-endemic levels of MRSA, the authors warn that the number of serious infections and deaths will likely increase if LA-MRSA CC398 spreads further into the general population.
May 30 Clin Infect Dis abstract


Maryland law ends routine use of antibiotics in healthy farm animals

Maryland has become the second state in the nation to prohibit the routine use of antibiotics in healthy livestock and poultry.

Reuters reports that Maryland's Keep Antibiotics Effective Act will take effect on Oct 1 and that farmers in the state will have until Jan 1, 2018 to comply with the law. Maryland's governor declined to sign or veto the bill last week.

Under the new law, farmers in the state will only be allowed to use antibiotics to treat sick animals or to control verified disease outbreaks. California passed a similar law in 2015 that will go into effect next year. Both laws go beyond the US Food and Drug Administration's guidelines, which aim to prevent the use of medically important antibiotics for growth promotion in food-producing animals but do not end their use in disease prevention. Critics have said the FDA policy doesn't go far enough.

"Maryland’s action to protect antibiotics sets the example for other states to follow," Emily Scarr, director of the advocacy group Maryland PIRG, which supported the law, said in a press release. "We hope more states, retailers, and producers will now become inspired to protect public health by taking action to restrict use of antibiotics on farms."
May 30 Reuters article
May 30 U.S. PIRG press release

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