After multiple people reported feeling sick after attending an August 18 party celebrating Baltimore Magazine’s Best of Baltimore, health officials began investigating a potential outbreak of campylobacter, a bacterial infection known to cause unpleasant symptoms.

Here are five things to know about campylobacter.

A campylobacter infection, or campylobacteriosis, is caused by a bacteria carried in animals and passed to people by undercooked meat or unpasteurized milk, for example, according to the U.S. Centers for Disease Control and Prevention.

It also can spread to people through unwashed fruits and vegetables contaminated by soil and water containing feces from infected animals. It can spread from pets and baby diapers, too.

Nationally, the CDC reports that it’s pretty common. There are about 20 cases diagnosed each year for every 100,000 people. Many more cases go undiagnosed or unreported, and the CDC estimates such infections affect closer to 1.5 million Americans every year.

In the state, the Maryland Department of Health reports the there were 720 cases in 2020, 892 in 2019 and 938 in 2018.

That’s far more than other bacterial infections in 2020, such as Legionnaires (184 cases) and listeria (14 cases) but more in line with salmonella (702 cases).

Campylobacter causes fever, stomach cramps, nausea, diarrhea and vomiting.

Some people have no symptoms. When symptoms arise, it’s usually two to five days after exposure and they last about a week, according to the World Health Organization.

WHO reports that infections can become severe in the very young and old. It can become deadly for those with compromised immune systems when the bacteria enters the bloodstream.

How is it diagnosed and treated?

The infection is confirmed with a lab test from stool or bodily fluids.

Most people recover without any antibiotics, but those with diarrhea should drink a lot of water to stave off dehydration.

Because it’s thought to be the most common bacterial cause of diarrhea in developed countries and universally infects children in developing countries, there are efforts to develop a vaccine. Candidates are still in early testing, according to the Johns Hopkins Bloomberg School of Public Health’s Center for Immunization Research.

Who is investigating the Best of Baltimore event?

The magazine reported potential cases to health officials when they learned of them in the days after the event. The Baltimore City Health Department is leading the investigation but working with the Maryland Department of Health.

State health officials said they sent out a survey to party attendees regarding illnesses.