Legionnaires’ disease has been reported in a handful of states this summer and fall. Now, an outbreak of the disease has killed an eighth person in Illinois, and sickened 41. The cases are mostly confined to a veterans home, health and veterans affairs officials report.

All unrelated cases are part of a typical pattern observed in a disease that tends to appear in warm weather, and is mostly dangerous for people who already are sick or weakened.

The Illinois outbreak (Quincy, about 240 miles southwest of Chicago), comes after recent outbreaks of the respiratory illness that killed a dozen people in New York City and sickened inmates of a California prison.

Such outbreaks have become more common in recent years, but experts are uncertain if that’s because of better reporting or surveillance, or on the other hand, if the disease, a type of pneumonia, is truly becoming more prevalent, said Dr. Matthew Moore, a medical epidemiologist at the federal Centers for Disease Control and Prevention.

Here’s the list of recent Legionnaires’ outbreaks:

—In Illinois, an outbreak at the Illinois Veterans Home in Quincy, an assisted living and nursing home southwest of Chicago, has led to the deaths of eight elderly residents, all with underlying conditions. Another 32 residents have been sickened. Tests were pending Tuesday for other residents. The source has not been identified, said Ryan Yantis, a spokesman for the state’s Department of Veterans Affairs.

—In California, six inmates at San Quentin State prison have been diagnosed with the disease since last week; five others are hospitalized with pneumonia-like symptoms and 73 inmates are under observation and being treated for respiratory illness in a prison medical unit, said prisons spokeswoman Dana Simas. Authorities have not found the source.

—In New York, an outbreak in July and August that killed 12 people and sickened more than 100 was traced to bacteria found in an air-conditioning unit cooling tower at a Bronx hotel.

—Two isolated illnesses occurred—one at Illinois’ Stateville prison last month, the other in July at West Chester University in Pennsylvania.

—High levels of Legionella bacteria were found last week in the water system at a substance abuse treatment unit in Arizona at the Phoenix Veterans Affairs Health Care System, leading authorities to relocate 20 patients. The bacteria were discovered during routine testing and no illnesses have been reported, spokeswoman Jean Schaefer said.

—A building at a GlaxoSmithKline drug manufacturing plant in Zebulon, N.C. was closed temporarily in August after Legionella bacteria were found in the external cooling towers there; no one was sickened.

What is Legionnaires’ Disease?

The illness is a type of pneumonia caused by bacteria that infect the lungs.

Named after a 1976 outbreak among participants of an American Legion convention in Philadelphia, the disease can cause coughs, breathing trouble, fever and muscle aches. The elderly and people with chronic illnesses are most at risk.

Antibiotics can treat the disease but it is fatal for between 5 percent and 30 percent of patients, Moore said.

Photo: Gram-negative bacilli of Legionella pneumophila from a buffered charcoal-yeast extract (BYCE) culture. L. pneumophila is the aetiological agent of Legionnaire’s disease. Credit Geoffrey Ridgway, Wellcome Images

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