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Biological Health Hazard – Rare zoonotic pathogen |Streptococcus zooepidemicus, (Outbreak – Fatal): King County, Washington, USA


Published Date: 2016-08-05 13:12:34
Subject: PRO/AH/EDR> Streptococcus zooepidemicus – USA: (WA) fatal
Archive Number: 20160805.4395408

Date: Friday 5 August 2016
Source: CDC. MMWR Morb Mortal Wkly Rep 2016; 65(30): 788 [edited]

Kawakami V, Rietberg K, Lipton B, et al: Notes from the field: Fatal infection associated with equine exposure — King County, Washington, 2016
On 17 Mar 2016, Public Health–Seattle & King County in Washington [State] was notified of 2 persons who received a diagnosis of _Streptococcus equi_ subspecies zooepidemicus (_S. zooepidemicus_) infections. _S. zooepidemicus_ is a zoonotic pathogen that rarely causes human illness and is usually associated with consuming unpasteurized dairy products or with direct horse contact (1). In horses, _S. zooepidemicus_ is a commensal bacterium that can cause respiratory, wound, and uterine infections (2). The health department investigated to determine the magnitude of the outbreak, identify risk factors, and offer recommendations.

Patient A, a previously healthy woman aged 37 years, operated a horse boarding and riding facility in King County, Washington. Patient A fed, groomed, and exercised the facility’s 6 horses and cleaned the stalls daily. During the week of 21 Feb 2016, patient A developed mild pharyngitis and cough. During the week of 21 Feb 2016, horse A developed mucopurulent ocular and nasal discharge and lethargy. On 29 Feb 2016, patient A began administering 10 days of sulfa-based antibiotics to horse A, which recovered without incident.

Patient B, a previously healthy woman aged 71 years and the mother of patient A, developed symptoms consistent with an upper respiratory infection during the week of 21 Feb 2016 while visiting patient A and living in the same household. On 2 Mar 2016, she developed vomiting and diarrhea. On 3 Mar 2016, she was found unconscious and transported to a hospital, where she died that day. Patient B had close contact (that is, riding, petting, and walking) with horse A on at least 25 Feb and 29 Feb 2016.

Culture results of nasal swabs collected on 10 Mar 2016 from horse A and 2 other horses that appeared well were positive for _S. zooepidemicus_. Patient A did not report consumption of unpasteurized dairy products or exposure to other animals, apart from one healthy cat, during the preceding 2 months. A throat culture from patient A obtained 10 Mar 2016 and blood cultures from patient B grew _S. zooepidemicus_ isolates indistinguishable by pulsed-field gel electrophoresis from isolates cultured from horse A and a 2nd horse at the facility. _S. zooepidemicus_ cultured from a 3rd horse did not match other isolates.

The epidemiologic and laboratory evidence from this investigation linked a fatal _S. zooepidemicus_ infection to close contact with an ill horse. Patient B might have been at increased risk for invasive disease by _S. zooepidemicus_ because of her age and her possible antecedent upper respiratory infection. Because patient A specifically sought health care and a throat culture as a result of patient B’s death, determining whether the _S. zooepidemicus_ infection preceded or followed her mild illness approximately 2 weeks earlier was not possible.

Although _S. zooepidemicus_ is a rare zoonotic pathogen in humans, older persons might be at increased risk for a fatal outcome from this infection; in 32 reported cases, the median age was 61 years (range = less than 1 to 83 years) with 7 deaths (case-fatality rate = 22 percent) (1). Consistently practicing thorough hand washing with soap and water after contact with horses and other animals or areas where animals are housed is recommended (3). This outbreak highlights the need for more research regarding risk factors for zoonotic transmission and spectrum of human illness associated with _S. zooepidemicus_.

1. van Samkar A, Brouwer MC, van der Ende A, van de Beek D: _Streptococcus equi_ meningitis. Clin Microbiol Infect 2016; 22(1): e3-4.
2. Clark C, Greenwood S, Boison JO, Chirino-Trejo M, Dowling PM: Bacterial isolates from equine infections in western Canada (1998-2003). Can Vet J 2008; 49(2): 153-60;
3. CDC. Wash your hands. Atlanta, GA: US Department of Health and Human Services, CDC; 2016;

Communicated by:

[The state of Washington can be located on the HealthMap/ProMED-mail interactive map at King County can be seen on the map at

_Streptococcus zooepidemicus_ is normal flora of the upper respiratory tract of horses, but can cause lower respiratory tract infection as part of a polymicrobial anaerobic infection with Gram-negative and anaerobic pathogens (see reference 2 above). It also causes wound and uterine infections in horses and infections in other domestic animals such as cattle, sheep, goats, pigs, dogs, and cats ( In cows, goats, and sheep, _S. zooepidemicus_ can cause mastitis.

Occasionally _S. zooepidemicus_ has caused human infection linked to contact with horses or consumption of unpasteurized dairy products. These infections, which frequently have been severe ( and even fatal in some instances, include septicemia, endocarditis, septic arthritis, pneumonia, meningitis, as well as post streptococcal glomerulonephritis (

_S. zooepidemicus_ is an encapsulated, Gram-positive coccus that grows in pairs or long chains. It is a large colony, beta-hemolytic group C streptococcus and has a surface protein that impedes phagocytosis like the M-protein of group A streptococci. _S. zooepidemicus_ is highly susceptible to penicillin, but is frequently resistant to trimethoprim sulfamethoxazole. Whenever group C streptococci are recovered from severely infected people, speciation should be considered for appropriate epidemiologic investigation, because identification of the pathogen as _S. zooepidemicus_ would imply a zoonotic origin. – Mod.ML]

See Also

Streptococcus zooepidemicus, canine – Canada 20130303.1569085

Streptococcus zooepidemicus, equine – Iceland 20101223.4518

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ProMED-mail is a program of the International Society for Infectious Diseases

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