Solving the Mystery of Legionnaire's Disease

In 1976, the Stratford Hotel in Pennsylvania held a convention for the Pennsylvania chapter of the American Legion. Just after the convention, 221 of the attendees got sick with a strange case of pneumonia. Seventy-two of them died.

Photo via 36th Infantry Division

They provided the name for a culprit that had been killing for thousands of years, and had been studied for decades.

Legionnaire's Disease caused quite a health scare when it first came to light. After a convention of the American Legion, with over 2000 attendees, different legionnaires began to get sick. The symptoms, fever, coughing, and difficulty breathing, came on just days after the beginning of the convention, but the deaths dragged on for months. The convention had been in August, and by the end of the fall, one third of those infected had died. Those were nightmare rates of fatality, and people wanted to know what was causing them.

At the time, there was the added confusion of a very recent influenza outbreak with similar symptoms, and so it was only when the CDC turned a sample of tissue over to Dr Joseph McDade that they finally got a break. He was studying bacteria, but was asked to help in ruling out a certain kind of fever. After ruling it out, he experimented a little with guinea pigs and antibiotics. When he noticed some strange bacteria in the guinea pig tissue, he finally isolated the cause of Legionnaire's Disease - a strain of bacteria since called Legionella pneumophila. After a some searching, the CDC found it in the cooling tower of the air conditioning of the hotel.

Solving the Mystery of Legionnaire's Disease

A new mystery, which replaced the old, was how exactly this bacteria had remained harmless for so long and then suddenly caused so many infections and deaths. The answer was, it had not. Eleven years before the Stratford Hotel incident, it had caused 14 deaths in a psychiatric hospital in Washington. Nine years before that, seventy-eight workers at a meatpacking plant went to the hospital with a mysterious case of pneumonia.

Both outbreaks remained mysteries for the same reason. Legionella isn't the proto-pandemic it appeared to be when it made headlines in 1976. It only grows in very specific conditions. McDade found the bacteria in part because guinea pigs are particularly susceptible to the bacteria. Mice, which the rest of the CDC was using, were not. Streams and public water systems are also not. The bacteria need temperatures of between 95 and 115 degrees, which is why they're generally found in hot springs. It's likely that people have been getting this disease from dips in hot springs for thousands of years.

Solving the Mystery of Legionnaire's Disease

Legionnaire's Disease is likely most infectious when, as it did in 1976, it gets into the air conditioning system. The bacteria are dispersed in the water in the system, and sprayed as aerosol drops over everyone in the building. People inhale them into their lungs, where the bacteria do the most damage.

It's not just air conditioning systems that cause the problem. Hot tubs and jacuzzis, with their warm temperatures and heavy steam rising up, also cause a lot of outbreaks. Anywhere there is a lot of warm water that people breathe into their lungs, there is the potential to inhale Legionella pneumophila. Fortunately, it's not the killer that the first known outbreak made it seem. Many people who get infected get what's known as Pontiac Fever - nothing more than an unpleasant fever and a lot of coughing. Some health officials think that, if anything, Legionnaire's Disease is so mild that it's often under-reported.

Lab and Lung Tissue Images from the CDC.

[Via Bacteria, TribLive, NCBI, BBC, WHO.]