An outbreak of intestinal disease that began last year and made its way to Portland's homeless population sickened at least 103 people in Oregon and forced public health workers to spend months working to stop the spread.

Cases of shigella, which causes severe diarrhea, first appeared last summer in men who have sex with men. Public health workers began investigating and notifying healthcare providers. Soon after, cases showed up in the local homeless population.

That news came Thursday in an article published in a national health journal.

Workers from the Multnomah County Health Department and Oregon Health Authority wrote the article, which appeared in the Centers for Disease Control and Prevention's Morbidity and Mortality Weekly Report.

Shigella is spread by oral contact with fecal matter. The disease is highly contagious, and transmission can occur through consumption of contaminated food or water, touching contaminated surfaces, or sexual contact.

Of 103 total cases tracked from July 2015 through May 2016, 46 people were hospitalized. No deaths were reported.

When the county health officials learned of the first cases, involving men who have sex with men, they said they targeted that population with educational materials.

But in October 2015, a case appeared in a man who described himself as homeless and also as having sex with men. Then, from November through January, several cases began cropping up in the county's overall homeless population.

"Once we realized it had entered the homeless population," deputy health officer Dr. Jennifer Vines said, "we really geared up with a lot of partners."

Homeless outreach workers and health department staffers visited shelters and camp sites to distribute educational materials and hand-sanitizing wipes, according to the county.

Disease outbreaks among the homeless are rare in Multnomah County, Vines said, but can be especially serious because of the lack of access to sanitation.

Asked why the county didn't send a mass alert during the outbreak, spokeswoman Julie Sullivan-Springhetti said public health workers met daily with homeless services providers and stayed in frequent communication with the most affected groups of people.

-- Emily E. Smith

esmith@oregonian.com

503-294-4032; @emilyesmith