A mysterious sickness, a string of deaths and 2000 army vets

Put your detective caps on, for here is a story worthy of Sherlock Holmes.

It's Philadelphia 1976 and a string of people are dead with many others struck down with malaise, headaches, muscle aches, fevers, abdominal pain and what appears to be pneumonia. Many of those afflicted are army officers and war vets who recently attended a conference at the luxurious Bellevue-Stratford hotel.

At first health officials dismissed concerns of the Bellevue cases being anything out of the ordinary. After all, many of the affected cases were elderly war vets who were often heavy drinkers and smokers and had a range of underlying health problems, so a few deaths were not unusual.

But two weeks and a flurry of similar reports later, and concerns and cases had escalated with 182 cases and 29 deaths across the state. The public was in a panic, fuelled by wild theories circulating in the press as health officials scrambled to provide an explanation to the mystery.

Could there be a connection with a deadly outbreak of swine flu which had swept through an army base in New Jersey, just 66 km northeast of Philadelphia, earlier in the year? Was it some other deadly disease like psittacosis (or "Parrot Fever") or maybe Q-fever? Could there be some form of foul play perhaps by anti-war radicals? Or was there some other explanation?

By now, the detectives (aka health officials from the CDC Special Pathogens Branch and Epidemic Intelligence Service) were on the case. The first part of the detective work and scientific process was to come up with a definition of the sickness to classify if people were ill with the Bellevue sickness or not. Next, they needed to look at the number of people who were exposed and identify the number who got sick and the number who were not sick (known as controls). And, of course, the detectives needed to do their research of the case details: names, age, address, days at conference, medical info, date sick, cause of death... This was a massive job and involved over 30 specially trained health officers.

The investigation soon found that some 4500 guests (2000 delegates of the American army legion and their families) had attended the convention at the Bellevue, as well as hotel staff. Most of those afflicted with illness were army delegates who attended the convention and stayed at or visited the Bellevue lobby and suites. Other cases included one of the hotel contractors (an air con repair man), a bus driver and a few pedestrians who had passed by the hotel (but not come inside).

The detectives also discovered ill patients had spent on average 4-5 hours more time in the hotel than the healthy controls, and more time in the lobby. However, this was not true for hotel staff who had spent the same amount of time or more in the lobby. In a similar conundrum, two-thirds of ill patients had drunk the hotel water, making them more likely to have drunk the water than controls. Yet, hotel staff frequently drank from the water fountain in the lobby, unlike many of the guests.

Early microbiology testing showed that the Bellevue disease was not the New Jersey swine flu or any other known strains of the virus. But this didn't rule out any other dangerous diseases and microbiology testing for these diseases could take weeks, possibly months.

So these findings brought further questions. Why hadn't any hotel staff (other than the air con contractor) got sick? Perhaps poisoning was the answer to that question, but then why had the pedestrians, who never even went inside the hotel, also been struck down?

To delve deeper, the chief investigators booked a room at the hotel and distributed surveys to all army officers in the Pennsylvania legion and other hotel guests and staff. They also brought in a team of homicide detectives to help shed some light on the darker suspicions of the case.

The detectives slowly eliminated some of the poisoning theories. For example, one of the favoured hypotheses centred on phosgene, an ideal poisoning agent because it quickly leaves the body without a trace. However, phosgene causes severe kidney damage and none of the patients showed any harm to their kidneys. Similarly, the chief investigator dismissed nickel carbonyl toxin as the metal rarely caused high fevers (as seen in the Bellevue cases) and had a much shorter incubation period than the Bellevue sickness. He also ruled out a waterborne illness and food poisoning, since the affected cases had bought food from many different sources, and hotel staff often drank the hotel water.

All hopes were now pinned on the microbiology studies.

But in November the health detectives were still at a loss. Political leaders were also frustrated at the lack of results, some saying the inconclusive investigation was a national "embarrassment". On the 10th November, after weeks of bad publicity, the hotel announced it was closing its doors. Soon after, the chief detective was forced to close the investigation unsolved. All the microbiology tests had come up blank, so the only thing health officials could say with any confidence was that the Bellevue case resembled an infectious disease and there had been no secondary spread.

A while later at a Christmas party, a guest came up to CDC scientist Joseph McDade (who had been studying the possibility of Q-fever in the Bellevue case) and told McDade that he was very disappointed in the CDC efforts to solve the Bellevue case. A worrier and perfectionist, the sorry feedback stuck with McDade and prompted him to revisit the Bellevue samples he had worked on.

When McDade revisited the samples, he decided to double check a peculiar rod-shaped bacteria that had puzzled when working on the active case. He had initially dismissed the elusive bacteria as a contaminant since he was the only scientist working on the samples to see them, but now he looked further and found a link with the Bellevue illnesses. It was the missing link everyone had been searching for!

McDade had helped discover a new bacteria dubbed legionella, which was not only linked to the Bellevue incident, but a series of prior unexplained illnesses/deaths such as the Rio Park case. After examining the various cases of legionella or Legionnaires disease, it quickly became clear that the illness was linked with hotels, hospitals and other large buildings and was likely spread through their cooling towers and air conditioning systems.

Though the Bellevue hotel had been closed and its air conditioning units cleaned out, the detectives concluded that the cooling system was responsible. The Bellevue had an old cooling system with a cooling tower on the roof that was exposed to the elements and susceptible to contamination and bacteria growth. In the cooling tower, the contaminated water is sprayed into droplets, and some of these can escape at the top of the tower and be released into air outside.

Weather records from the days of the Bellevue convention showed a sharp temperature inversion from the 22 July - 24 July meaning air near the hotel roof was warmer than at ground level (the opposite temperature gradient to usual). This allowed the contaminated water droplets to cascade down the side of the building and be sucked into air vents used by the air conditioners in the hotel lobby.

Though the air conditioning units couldn't be tested directly for legionella, detectives found legionella antibodies in the hotel staff explaining why the staff had not got sick. They had developed immunity after being exposed with minimal amounts of legionella from time to time.

The mystery was finally solved!

Other sources of interest:

The Pandemic Century, MARK HONIGSBAUM, 2020

The Philadelpia Killer, 1976

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