By Vance Kawakami, CDC Epidemic Intelligence Service Officer at Public Health – Seattle & King County

Last week, the Centers for Disease Control and Prevention Morbidity and Mortality Weekly Report discussed a recent, fatal Streptococcus equi subspecies zooepidemicus (Strep zooepidemicus) human infection contracted from close contact with a horse at a private horse riding and boarding facility in King County. The deceased individual was a healthy 71 year-old woman who had close contact with a sick horse (i.e., riding, petting, and walking) over several days prior to becoming ill. Samples from the patient and two horses at the facility (including the ill horse) grew identical bacteria, suggesting zoonotic transmission of this bacterium from the horse to the patient.

Public Health conducted an investigation and determined an additional four people were infected with the same germ but did not develop serious illness. We gave recommendations to the owner and customers of the facility to prevent any future infections.

This is a curious case, so let’s get down to basics. (Or, you can read the Seattle Time’s coverage and the full report here.)

What is Strep zooepidemicus?
Strep zooepidemicus is a bacterium that is commonly found on healthy horses and only occasionally causes disease in horses and other mammals.

How common is Strep zooepidemicus infections in humans?
From what we know about this bacterium, it rarely causes serious infections in humans. When human infections do occur, they are typically linked to close contact with horses or consumption of unpasteurized dairy products. The limited information about Strep zooepidemicus human infections suggests that older persons (65 years or older),  persons with a chronic medical condition, or those who are taking medication that may weaken their immune system may be at an increased risk of developing a serious infection.

I am concerned that I may be at a higher risk of developing a serious Strep zooepidemicus infection. What should I do?
Seek the advice of your healthcare provider to determine if you should take extra precautions around horses and other animals.

What steps can I take to prevent getting a Strep zooepidemicus?
The risk for a serious infection with Strep zooepidemicus associated with horse contact is very low, but out of an abundance of caution, we  recommend that you wash your hands often with soap and water or use alcohol-based cleaners if soap and water is not available, especially after contact with horses and other animals or areas where animals are housed. Avoid close contact with sick horses, especially if they are showing signs of a respiratory infection (e.g. sneezing, eye and/or nasal discharge).

I have horses. Do I need to have them tested for Strep zooepidemicus?
Because it is commonly found on healthy horses, you do not need to have them tested for Strep zooepidemicus. If you have any concerns about the health of your horses, please contact your equine veterinarian.