State health officials investigating a hepatitis A outbreak in southeast Michigan reported Thursday a concerning increase in cases among men who have sex with men.

So far in October, there have been 11 such cases, compared to a total of 10 over the preceding 14 months.

Officials are urging all men who have sex with men and others who are at risk to get vaccinated.

Read more:

FBI: 12 Michigan juvenile trafficking victims rescued, 8 pimps arrested

Since Aug. 1, 2016, there have been 457 confirmed cases of hepatitis A in the city of Detroit and Ingham, Lapeer, Livingston, Macomb, Monroe, Oakland, Sanilac, St. Clair, Washtenaw and Wayne counties reported to the Michigan Department of Health and Human Services. That figure represents a 14-fold increase in cases compared to the same period in 2014-15.

Eighteen people have died.

No single source has been identified.

"We are seeing a large person-to-person transmission. It's that not that we have one particular food source, or one specific drug" linking all the cases, said Angela Minicuci, a spokeswoman for the Michigan Department of Health & Human Services.

Hepatitis A attacks the liver and causes symptoms such as abdominal pain, nausea, vomiting, diarrhea, dark urine, clay-colored stool, fever, chills, and yellow skin and eyes (jaundice).

People affected by the outbreak have ranged in age from 20-87, with a median age of 42, according to the state health department. Most of them, 63%, are men. About 85.6% of the cases involved hospitalizations.

Among men who have sex with men, the hospitalization rate is higher — 95.2% — and the median age is 38.

State health officials said all men who have sex with men should get vaccinated, the same guidance provided by the national Advisory Committee on Immunization Practices.

"Despite this guidance, hepatitis A vaccination coverage among (men who have sex with men) in the United States remains low leaving many adult men unprotected. There are currently multiple hepatitis A outbreaks among (men who have sex with men) in the United States and Western European countries," reads a press release from the state health department.

In the overall outbreak, 48% percent of patients reported illicit drug use, 27.5% were co-infected with hepatitis C, and 3% were co-infected with hepatitis B. Additionally, 6% reported recent incarceration, and 7.7% of men reported having sex with men, according to state health officials.

Read more:

Michigan mom jailed over vaccine refusal: Don't give my son more shots

Time from exposure to onset of illness is typically 15 to 50 days. The illness usually lasts several weeks to several months.

People who have symptoms should immediately contact their doctors, officials said. They should also talk to their doctors about vaccination or immunoglobulin.

In recent months, hepatitis A cases have been linked to food workers in Ann Arbor; Grosse Pointe Woods and Grosse Pointe Park; and Mt. Pleasant.

The state health department has been working with local health departments to investigate cases and raise awareness about the disease and the importance of vaccinations. Those efforts include ongoing vaccination campaigns in the Macomb, Oakland and St. Clair jails, as well as in substance abuse treatment centers and homeless shelters. There are discussions about starting campaigns in the Detroit Receiving Center and the Detroit Detention Center.

Who is at risk

Along with men who have sex with men, the following people are considered at-risk:

• Health care workers who have direct contact with patients

• People who use injection and non-injection illegal drugs

• People who participate in commercial exchange of sexual practices

• People who are homeless or in transient living situations

• People who are or have recently been incarcerated

• People who have had personal contact (e.g., household, sexual) with hepatitis A patients

• Food handlers

• People with liver diseases, such as hepatitis B or hepatitis C.

Health department contacts

For information about receiving a hepatitis A vaccine, contact your local health department:

• Detroit Health Department, 313-876-4000

• Ingham County Health Department, 517-887-4316

• Lapeer County Health Department, 810-667-0448

• Livingston County Health Department, 517-546-9850

• Macomb County Health Department, 586-469-5372

• Monroe County Health Department, 734-240-7800

• Oakland County Health Division, 800-848-5533 or noc@oakgov.com

• Sanilac County Health Department, 810-648-4098

• St. Clair County Health Department, 810-987-5300

• Washtenaw County Health Department, 734-554-6700

• Wayne County Communicable Disease Unit, 734-727-7078

Contact Ann Zaniewski: 313-222-6594 or azaniewski@freepress.com. Follow her on Twitter: @AnnZaniewski.