CHICAGO (AP) — The timing is not the best. Immigration-rights rallies are set for Friday as health officials try to clamp down on a swine flu epidemic with roots in the same country as many of the expected demonstrators: Mexico.

Public health officials on Thursday had not advised canceling large-scale events unless they were specifically tied to an institution or location with a laboratory-confirmed case of the illness. They urged people to stay home if they are sick.

Organizers of the May Day rallies, which have drawn thousands and even hundreds of thousands of people in recent years, said they would look to recommendations from public health officials about whether to cancel or modify the events.

"We're monitoring the situation to make sure that anything that is going to be conducive to the health and safety of communities is observed," said Clarissa Martinez, a director for the National Council of La Raza.

Crowds on Friday were expected to be around the same as last year. In Chicago, which has had the nation's largest marches in recent years, about 15,000 participated in 2008. That's a dramatic drop from 2006, when more than 400,000 took to the streets.

Thousands also were expected at events Friday in Houston, Los Angeles, Miami, New York, Seattle and other cities. Health officials urged participants to use common sense, including washing their hands and avoiding people who are coughing or sneezing.

"Of course, anyone who doesn't feel well should stay home," said Melaney Arnold, a spokeswoman for the Illinois Department of Public Health. She added that she doesn't think the march should be canceled.

Some schools have closed because of the swine flu outbreak, and U.S. and Mexican officials have been urging migrant workers to take health precautions and get medical care if they feel sick.

The rallies come as illegal immigrants are being blamed on some conservative blogs and talk shows for spreading swine flu in the U.S. The outbreak is believed to have originated in Mexico, where there are 168 suspected deaths from the disease, before spreading to at least 10 other countries, including the U.S.

The only confirmed U.S. swine-flu death was of a Mexican toddler whose family was visiting relatives in Texas; many reported cases were among U.S. citizens who vacationed in Mexico.

"For people who like to blame Mexicans, they are going to blame us for everything no matter what," said Jorge Mujica, a labor union activist and organizer for Chicago's immigrant rights march. "We are not going to pay attention to that."

For most rally organizers, swine flu was secondary to promoting immigration reform, including pathways to citizenship for an estimated 12 million illegal immigrants — hopes buoyed with Barack Obama in the White House and a Democratic-controlled Congress.