Plague in the Big Apple: Rare cases trigger bioterrorism response

It was pneumonic plague until proven otherwise’

When a rare and deadly infection suddenly appears out of time and place, today’s clinician cannot exclude the possibility of bioterrorism. A case of plague (Yersinia pestis) had not been seen in New York City in more than a century. In November 2002, there appeared not one case, but two.

A couple from New Mexico, where the disease maintains a low endemic level in various animal hosts, traveled to New York City. Two days later, they developed fever and unilateral inguinal adenopathy suggestive of plague. In time, the telltale buboes — swollen lymph glands — would appear as the classic marker for bubonic plague. As the news got out, a newspaper headline warned that the "Black Death" had hit a city already deeply scarred by acts of terrorism.

Much like smallpox, plague resonates with grim historical overtones. The disease hardly needs large font headlines to invoke a visceral response. In a period of some five years in the 14th century, plague killed 25 million Europeans. Combine that with post-9/11 New York City, and you have the makings of a panic.

"New York citizens are very shaken, as you can imagine," says Beth Raucher, MD, hospital epidemiologist for Beth Israel Medical Center, the New York City hospital where the patients were admitted. "People are very brittle here. If you had seen some of the newspapers and web sites that published that first day — there were terrible headlines. We had to dispel a lot of that."

The couple, a 47-year-old woman and 53-year-old man, received gentamicin and other antibiotics in the hospital emergency department. Both patients were admitted and placed in respiratory isolation pending exclusion of pneumonic plague.

"We made the assumption that it was pneumonic plague until proven otherwise," Raucher says. "That is why we put both patients on strict isolation prior to finding out what their diagnosis was. I think if it is going to be used as a BT [bioterrorism] agent, it is going to be most likely in the pneumonic form."

The only form of plague transmissible from person to person, pneumonic plague occurs when Y. pestis infects the lungs. Transmission can occur if someone breathes in aerosolized bacteria, either from an infected person or, theoretically, during a bioterrorist attack using aerosolized plague. The World Health Organization estimates that if 50 kg of Y. pestis were released over a city of 5 million, pneumonic plague could occur in as many as 150,000 people — 36,000 of whom would be expected to die. Fatality rates would depend on various factors, including time between onset of symptoms and initiation of antibiotics, access to advanced supportive care, and the dose of inhaled bacilli. The fatality rate of patients with pneumonic plague when treatment is delayed more than 24 hours after symptom onset is extremely high.1

Bubonic plague — the most common form of the disease — usually occurs when an infected flea bites a person, serving as the vector between animal host (e.g., rat) and an infected human. Bubonic plague does not spread from person to person. Though bioterrorism could not be ruled out, the histories of the New York patients suggested natural causes. The couple reported being avid hikers and having a dead wood rat in their yard months earlier that tested positive for Y. pestis. Yet a confounding factor came with the determination that they could not have infected each other. Both people had bubonic plague.

"The issue for us was, why two infected people exactly at the same time?" Raucher says. "In our heart of hearts, I don’t think we ever really felt that it was bioterrorism, but we couldn’t exclude it. Bubonic plague is not transmissible from person to person. That is why this is such an unusual case. We guesstimate’ that they both got it at the same time from the same exposure on their property, which really would be very odd. It is a very low probability."

Bioterrorism alert sounded

As health officials in New Mexico were contacted to verify the exposure history, the hospital decided to roll out its bioterrorism response plans in case the disease was of nefarious origin. The plan emphasizes communication with external agencies, education, and assuring the safety of hospital patients, visitors, and staff.

"We decided to just go for it," Raucher says. "Because: a) it is going to be picked up by the media and there is going to be a lot of craziness surrounding this; and b) we just couldn’t be sure so we needed to get the health department involved."

The city health department was immediately contacted to assist with diagnostic testing, direct the public health response, and evaluate the potential that the two cases represented bioterrorism. Local health officials and the Centers for Disease Control and Prevention (CDC) were able to exclude pneumonic plague within 48 hours of the patients’ admission. The health department held a televised press conference to alleviate the fears of the public and relay information regarding plague transmission.

"One of the major things we learned during this was that a quick educational response is very important," Raucher says. "We did not have any breakdown of the health care system. The hospital went on, business as usual, because of a couple of things we did well. One was to put together an infection control newsletter very quickly on the topic. The infection control professionals did a lot of one-on-one discussion with a lot of people in radiology, food service, and the nurses in the [intensive care units]."

In addition, a letter explaining the situation to patients was placed on every food tray. "It said that these patients were in the hospital, they are under isolation, and it is not being spread," Raucher notes. "We’re a business. If people stop coming to the hospital, that would be a big problem."

She became a celebrity’

Still, the cases caused a media sensation, with reporters even trying to enter one of the patients’ rooms for exclusive interviews. "Because the woman wasn’t as sick, they were trying to get into her room," she says. "We had to place a security guard outside her room, and we had to put an extra security guard at the front door and close a lot of our entrances. She became a celebrity."

The wave of curiosity raised issues of confidentiality. The patients’ charts were removed from the normal medical rack so staff would not be tempted to peruse them. "The woman was in the hospital for just under a week," Raucher says. "She did really well. He was in really critical condition for quite a long time. He ultimately was discharged after about three months."

Health officials in New Mexico found that fleas from mice and rats near the home of the Santa Fe County couple tested positive for plague.

"There were positive fleas from mice caught in a landscaped area next to the patients’ home and also positive fleas from a mouse and a wood rat in an area about two miles from their home where they had hiked about a week before their onset of illness," says Paul Ettestad, MD, New Mexico state epidemiologist in Santa Fe. "There is convincing proof that the patients acquired plague around their home in New Mexico."

All of which raises another question — how do clinicians in New Mexico discern between naturally occurring plague and bioterrorism?

"We have a baseline level [of plague] that we are used to," says Joan Baumbach, MD, MPH, medical epidemiologist in the New Mexico health department in Santa Fe. "People present clinically fairly typically. In terms of hospital infection control, the chief concern is to rule out immediately any pneumonic component. We are very careful about that. We have an underlying endemic level in animals, so we have a pretty good baseline sense of activity [of animals with plague]. These people in New York had already been told about activity in their area, and they knew how it presented clinically."

That said, state bioterrorism planners still are wary of plague being used as an agent, she emphasizes. "We err on the side of including [bioterrorism] in our thinking, but it is really not difficult to recognize fairly typical situations from something that might be atypical," Baumbach says. "We tend to see bubonic cases a lot more frequently. You take their history and look for the risk factors [e.g., exposure to animals]."

Reference

1. Inglesby TV, Dennis DT, Henderson DA, et al. Plague as a biological weapon: Medical and public health management. JAMA 2000; 283:2,281-2,290.