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Outbreaks, Alerts and Hot Topics

February 2019

Brucellosis Related to Raw Milk Consumption

Mary Anne Jackson, MD | Interim Dean - UMKC School of Medicine | Medical Editor, The Link Newsletter 

Clinicians should be aware of recent human brucellosis cases in the United States caused by an antibiotic-resistant RB51 bovine vaccine strain and related to raw milk consumption. The most recent case was traced to Miller’s Biodiversity Farm in Quarryville, Pa. Described as a private food club and authentic Amish family farm in Lancaster County, the business offers over 300 products with direct home shipping, including raw milk products and some direct sales at group settings.  

Brucella abortus RB51 is a live-attenuated bacterial vaccine strain that has been used in cattle since February 1996. It is typically administered to non-pregnant female cattle 4 to 12 months of age. Typically, the vaccine strain is cleared from the blood of cattle within three days of vaccination, but in rare cases the animal may not clear the organism, and the vaccine strain may be shed in milk.

Human brucellosis cases previously have been reported associated with accidental exposure to the RB51 vaccine strain from needle stick injuries (MMWR Morb Mortal Wkly Rep. 2018 Jul 6; 67(26): 747), and in those exposed by spray exposure to eyes and open wounds. In 1997, nine individuals in Manhattan, Kan., were exposed to aerosolized infected material when caring for a vaccinated heifer who died after developing vaccine-associated brucellosis; eight were given post-exposure prophylaxis (PEP) and none developed disease (MMWR Morb Mortal Wkly Rep. 1998 Mar 13;47(9):172-5).

Potential exposures have been reported in 19 states: Alabama, California, Connecticut, Florida, Georgia, Iowa, Maryland, Massachusetts, Michigan, Minnesota, Mississippi, New Jersey, New York, North Carolina, Ohio, Pennsylvania, Rhode Island, South Carolina and Virginia. After the first two cases, which initially did not appear to be linked, occurred in Texas and New Jersey in 2017, the Centers for Disease Control developed a webinar to promote awareness of the risk of RB51 disease from raw milk exposure. The content emphasized that the RB51 strain is resistant to both penicillin and rifampin, which are often used for prophylaxis and described appropriate disease recognition, post-exposure prophylaxis (PEP) and outlined diagnostic and treatment recommendations. (https://www.cdc.gov/brucellosis/clinicians/rb51-raw-milk.html).

The most recent case was reported in a New York state resident in November 2018; milk samples from the Miller’s Biodiversity Farm dairy were also reported to be positive for RB51 and a health alert network communication was distributed (https://emergency.cdc.gov/han/han00417.asp ). The alert included recommendations for 21 days of doxycycline plus trimethoprim/sulfamethoxazole for PEP, that blood cultures be obtained in anyone exposed with symptoms, and that the laboratory must be informed so that appropriate precautions could be used to prevent laboratory exposure.

Human cases associated with raw milk consumption and caused by B. melintensis and B. abortus are usually acquired in a country where brucellosis remains endemic (e.g., Mediterranean Basin, Mexico, South and Central America, Eastern Europe, Asia, Africa, the Caribbean and the Middle East). Exposure to other Brucella species in hunters exposed to infected animals, e.g., wild hog, elk, bison, moose, caribou hunters and for certain occupational workers (e.g., slaughterhouse, meat-packing employees, veterinarians, laboratorians), is less common. Rarely, cases have been related to infected marine mammal exposures. Of the approximately 100 to 200 cases that are annually reported to the CDC, 70 to 75% are related to ingestion of raw milk, 25-30% to feral swine infection in hunters or after ingestion of infected swine meat (B. suis) and rarely, in cases occurring following sexual contact or laboratory exposure.

Clinical disease develops five days to six months (average two to four weeks) after exposure and symptoms may be remitting. Acute symptoms are typically flu-like with fever, headache, back pain, myalgia and arthralgia commonly reported. Lymphadenopathy and splenomegaly occur in 10 to 30% of cases. Arthritis and spondylitis are notable acute manifestations and endocarditis, meningitis and osteomyelitis are the most serious complications. Infected pregnant women may experience spontaneous abortion in the first and second trimesters; transplacental and breast milk transmission may occur. Neonatal disease typically has a sepsis presentation with progressive disease manifesting with hepatosplenomegaly and lymphadenopathy on examination.

Laboratory findings are nonspecific, but often include various cytopenias; some patients develop pancytopenia. Diagnostic testing should include blood culture; bone marrow culture is more sensitive (remember to alert the laboratory). Blood or tissue for PCR testing may provide rapid detection, but is not routinely available. While serology is available for B. melintensis, B. abortus and B. suis, it is most helpful for acute cases. It is not available for B. canis or RB51 and false positive testing may occur. 

Treatment generally involves combination therapy for six weeks with rifampin plus doxycycline, or trimethoprim/sulfamethoxazole with surgical debridement in some cases. Longer treatment courses of up to six months and up to three drugs (addition of gentamicin for first two weeks) are necessary for the  seriously ill patient with complicated disease.

In the current outbreak, raw milk from Miller’s Biodiversity Farm has been recalled, alerts have been sent to ensure consumers discard any purchased raw milk products, and for those exposed, PEP and treatment recommendations are published. The AAP Committee on Infectious Diseases released a report in January 2014, noting that sale of raw milk products was still legal in 30 states and confirmed the risk of raw milk consumption for transmission of Listeria, Campylobacter, Salmonella, Escherichia coli 0157 and Brucella species (Pediatrics. 2014 Jan;133(1):175-9. doi: 10.1542/peds.2013-3502. Epub 2013 Dec 16).