Reported cases of Legionnaires’ disease in the United States have jumped more than 260 percent since 2000, but the true number could make annual cases of the disease more common than brain cancer, leukemia or HIV, a Tribune-Review investigation has found.
The Centers for Disease Control and Prevention recorded fewer than 400 cases of the deadly form of pneumonia in the 1990s. Then in 2000, the cases exploded to 1,100. By 2011, about 4,200 cases were reported, according to CDC figures obtained by the Trib.
“When I first saw the figures (on new cases), they were startling,” said Janet Stout, a Legionnaires’ expert and director of the Special Pathogens Laboratory in Pittsburgh.
Yet foreign research obtained by the Trib shows that the Legionnaires’ cases reported to the CDC probably represent less than 5 percent of the actual cases. For years, researchers and health officials have estimated the disease probably affects 8,000 to 18,000 Americans a year based on a 22-year-old study of incidence rates in two Ohio counties.
Paul Edelstein, director of the University of Pennsylvania’s Clinical Microbiology Laboratory and a leading Legionnaires’ researcher, told the Trib that the true number probably ranges between 56,000 and 113,000 cases annually, based on an incidence ratio of 180-360 cases per 1 million people reported from extensive testing by German scientists. He said another recent study by foreign scientists estimated annual Legionnaires’ cases at about 90,000.
By contrast, new cases of HIV in the United States have averaged about 50,000 a year or less since the mid-1990s.
And even those recent study estimates may fall short of the actual mark. Edelstein said studies have shown that common tests may not detect as many as 40 percent of actual Legionnaires’ cases, yet the disease is the second-leading cause of people with pneumonia being admitted to hospital intensive care units nationwide.
“I think there are a lot of unrecognized Legionnaires’ cases,” he said. “A lot of people die of Legionnaires’ disease thinking they can cure it with chicken soup or whiskey.”
The debate now among scientists is whether the increase in reported cases and estimates reflects a new awareness of the disease by physicians, a sinister surge in the disease or a combination of both.
The bottom line, however, is that Legionnaires’ is not a rare disease. In fact, Legionella are such a common waterborne bacteria that they can be found in many homes and other buildings where water systems have stagnant sections or the water heater is not set properly. The bacteria also can be found in cruise ship hot tubs.
Despite the Legionnaires’ outbreak that sickened 21 patients, killing five of them, in VA Pittsburgh hospitals between February 2010 and November 2012, the disease does not affect only veterans or the elderly. The Trib’s review of Legionnaires’ cases reported to the CDC found half the cases involve people younger than 60.
Underestimated and misunderstood
The significant growth in CDC cases in the past decade “is a completely unexplained phenomenon,” said Joseph Vogel, a molecular biologist at Washington University in St. Louis who specializes in Legionnaires’ research. “The same tests are being used, so that does not explain it.”
“There may be other reasons, but I think its (incidence) is definitely increasing,” said Stout, who once worked in the Pittsburgh VA researching Legionnaires’.
A problem facing physicians is that the disease can be hard to diagnose. Edelstein agreed with a research paper that states common urine tests for Legionnaires’ could miss as many as 40 percent of cases. The paper, “Legionella and Legionnaires’ Diseases: 25 Years of Investigation,” adds that Legionnaires’ cannot be differentiated from other types of pneumonia on X-rays, and patient complaints often are identical.
That left most cases of Legionnaires’ to be treated like other pneumonias — a deadly mistake, experts say. Common antibiotics such as penicillin are ineffective.
Physicians treating patients with hospital-acquired pneumonia often suspect the illness is an infection caused by a superbug treated differently from Legionnaires’, said Dr. Joseph S. Cervia, a Legionnaires’ expert and clinical professor of medicine and pediatrics at Hofstra North Shore-LIJ School of Medicine in Hempstead, N.Y.
As a result, patients would receive antibiotics that would not be effective against Legionella, he said.
“For example, the staph infection MRSA is frequently treated with the drug vancomycin,” Cervia said. “This drug is not used to treat Legionella.”
A brief history
Although many people believe Legionella bacteria first popped up in 1976 at an American Legion Convention in Philadelphia, varieties of the pathogen were linked to outbreaks nearly 20 years earlier and probably have been around for more than 10,000 years, Edelstein said.
The first known Legionnaires’ outbreak occurred in 1957 in an Austin, Minn., meat packing plant, according to an article in the American Journal of Epidemiology. However, doctors at the time could not determine what sent 78 workers to the hospital.
The disease showed up again in St. Elizabeth’s Psychiatric Hospital in Washington in 1965. Eighty-one patients developed pneumonia from an unknown cause and 14 died. Disease hunters were baffled and pointed to an open window as a possible explanation.
But when American Legion members began dying in 1976, media throughout the nation sounded the alarm. Something new, deadly and unknown seemed to be on the loose.
Between Christmas and New Year’s Eve in 1976, scientist Joseph McDade had a brainstorm, according to a 1988 account in Clinical Microbiology Reviews. McDade determined he had been using the wrong technique to grow the Legionella bacteria from Philadelphia in eggs. He used a new method, and suddenly there it was: L pneumophila. (The L stands for the genus Legionella, and pneumophila refers to the species.)
Word spread, and many research centers began looking into the culprit and its tiny microbial relatives. One of those centers was the Pittsburgh VA, where an outbreak infected more than 100 people from 1978-82.
During that same period, the largest known outbreak occurred in the Wadsworth VA hospital in Los Angeles, where 218 were infected.
Some scientists thought a possible factor was a Carter administration conservation order to turn down hot-water temperatures in federal buildings during a national energy crisis, according to Stout and George Garrity, a professor of microbiology and molecular genetics at Michigan State University, both of whom worked on the problem in the early 1980s.
Legionella bacteria prefer hot-tub-like temperatures of between 95 and 115 degrees. But at temperatures about 131 degrees, they begin to die.
Edelstein discounts the Carter conservation measures as a cause for a rise in Legionnaires’ cases, pointing out the disease also was hitting private hospitals.
Scientists interviewed by the Trib agree the significance of the 1976 discovery was not fully understood. One early report in Clinical Microbiology Reviews appeared somewhat dismissive of Legionnaires’ in the original cases:
“We were spared the ‘monster killer’ that was constructed by the press in 1976, only to have it appear a few years later in the form of human immunodeficiency virus and acquired immunodeficiency syndrome.”
Today, there’s a much more complicated picture than anyone realized in the 1970s. Scientists have discovered more than 55 species of Legionella, more than 20 of which are linked to the disease. Most human disease is caused by Legionella pneumophila. However, that species is divided into at least 15 subgroups, called serogroups.
Of those, serogroup one causes the most pneumonia cases though the other serogroups are still dangerous. However, the urine test most commonly used to detect Legionnaires’ throughout the nation tests only for Legionella pneumophila serogroup one.
Exactly how deadly is Legionnaires’ disease is another question without an agreed upon answer, said Washington University’s Vogel.
When the disease is acquired in a hospital, some researchers estimate the death rate is more than 25 percent. All appear to agree that community-acquired Legionnaires’ disease is deadly by less than half that percentage.
The CDC simply places the disease’s death rate between 5 percent and 30 percent.
Staff writer Luis Fábregas contributed to this report. Lou Kilzer is a staff writer for Trib Total Media. He can be reached at 412-380-5628 or [email protected].