TORONTO - Over the last decade or so, thousands of people in North America have had to endure rabies shots after waking up to discover an uninvited roommate - a bat.
But a new Canadian policy aims at taking a more judicious approach to such events, based on an analysis that shows the risk of contracting the fatal disease is vanishingly low when there is no known contact between a bat and a sleeping person.
In a nutshell, as many as 2.7 million people could need to be vaccinated in order to prevent a single person from developing rabies from a so-called bedroom exposure in Canada, a study led by researchers at the Quebec Institute of Public Health shows.
The analysis further reveals it would cost as much as $2 billion for the vaccine, and would require the manpower equivalent of between 293 and 2,500 health-care professionals working full time for a full year to prevent that one case.
It's not sustainable, nor is it good policy, suggests Dr. Gaston De Serres, a medical epidemiologist with the institute and Laval University who is first author of the study.
The analysis is based on a telephone survey in which 36,445 Quebecers were asked about bat exposures. The resulting paper was published last year in the journal Clinical Infectious Diseases.
"When we did calculate what is the frequency of bat rabies due to bedroom exposure we should expect in our province, it was basically one case every 360 years," De Serres says.
With numbers like that, it might seem apparent that it doesn't make sense to vaccinate people who were in a room with a bat just because they weren't awake and therefore can't be absolutely sure they weren't scratched or bitten.
And after studying De Serres' analysis, Canada's National Advisory Committee on Immunization concluded just that. NACI, as it is called, recently issued a new guideline to cover these "bat in the bedroom" situations.
The old policy said rabies shots should be given whenever a bat was found in the room of a child, someone who is cognitively impaired or a sleeping person, unless the bat was caught and tested negative for rabies. The new one suggests people not try to catch bats, because studies have shown between two and five per cent of bats caught in homes are positive for rabies.
Furthermore, it suggests shots only be ordered if two conditions are met.
There's got to be a direct hit - the bat touched or landed on the person. And the policy says health-care providers should consider vaccinating then only if it cannot be ruled out that a bite or scratch occurred or that bat saliva might have come in contact with a wound or the person's mucus membranes.
With children, the new policy exercises more caution than it does with adults, says Dr. Joanne Langley, NACI's chair. Children should be vaccinated after any direct contact with a bat.
There is no change to the recommendation that people known to have been bitten or scratched by a bat or another potentially rabid animal get rabies shots. About 3,000 people a year get the inoculations, says the Canadian Centre for Occupational Health and Safety.
"On face value, it might be a little bit frightening," Langley, a pediatric infectious diseases expert at the IWK Health Centre in Halifax, admits of the decision to dial down the precautionary response.
"But as you sift through the information, you become familiar with it, you ... (see) how we got to this position where we're giving so many people this vaccine based on what was probably not very good data in the first place."
Still, it's not hard to see how the policy came about. In the early 1990s, there was a slight uptick in human cases of bat rabies in the United States. The numbers were small. But with a disease for which there is no treatment, any case is too many.
In addition, analysis there showed that of 21 U.S. cases that occurred between 1980 and the time of the decision, most victims either didn't think they'd been bitten by a bat they had encountered or couldn't recall encountering one at all.
The American equivalent of NACI, the Advisory Committee on Immunization Practice, decided in 1999 that people who had been in a room with a bat and who might be unaware they had had direct contact with the bat could be considered for what is known as rabies post-exposure prophylaxis or PEP - a regimen comprising one shot of rabies immunoglobulin (antibodies) and five shots of rabies vaccine.
NACI followed suit.
The thinking was that heavy sleepers or even people who'd been drinking alcohol before bed might not be roused by a bat bite or scratch.
But this abundance of caution, embraced with the best of intentions, has placed a heavy burden on public health and infectious disease doctors.
"All infectious disease doctors have been contacted by other clinicians, emergency room doctors, nurses, worried family members, friends about this issue," says Dr. Paul Sax, an infectious diseases specialist at Brigham and Women's Hospital in Boston.
"It's impossible to risk stratify. And that's where the dilemma comes in."
People panic, suggests Sax, who is also editor-in-chief of Journal Watch, a service which monitors and synthesizes medical research for doctors and health professionals.
"I can tell you anecdotes of people who've requested rabies immunization on the most absurd potential exposures. And they're really inconsolable," he says, citing a case of a person who wanted rabies shots after being pooped on by a squirrel while climbing a tree.
"In some ways it's easier to give the immunization than to counsel the individual about how low the risk is. And then furthermore, one does not want to be the clinician who makes the decision to withhold the immunization on those handful of cases that do occur," says Sax, who lauded De Serres' study on his Journal Watch blog, listing it as a "must read."
The paper was also cited as one of the 10 best of the year at last fall's annual meeting of the Infectious Diseases Society of America.
A rabies expert with the CDC acknowledges the bedroom exposure policy hasn't been universally welcomed.
"There has been a lot of controversy around that issue of being too inclusive," says Jesse Blanton, the CDC's co-ordinator for rabies surveillance.
And he admits that at times, the policy may have been over-applied, with people overlooking the "should be considered" part of the recommendation.
"Our recommendations aren't carte blanche that a person who wakes up with a bat (in the room) should receive PEP, but that it certainly should be considered by a physician or whoever the primary health care that the person is seeing," Blanton says.
Except for where it's clear there has been a bite or scratch, the CDC's intention is that cases be assessed with the help of state or local health departments, he says.
"Our definitions on paper are more inclusive. But because we do make these recommendations that there should be careful risk-benefit analysis and direct consultation with the state and local health department, we put a lot more of the onerous job on our state and local (officials) and even here at CDC."
De Serres says the argument for the new policy isn't about saving money, it's about not exposing people to a potentially risky intervention - rabies shots - they are very unlikely to need. Like any vaccine, rabies shots can cause side-effects, including the potentially fatal allergic reaction known as anaphylactic shock.
"For me to save money is not my purpose. I think that if we save money but at the same time we have lots of disease it's not good," says De Serres.