Outbreaks in two Toronto-area hospitals of a dangerous new form of superbug has infection-control experts contemplating a worrisome future.
Both outbreaks are now over. Details of the chains of spread and how the hospitals managed to stop them are outlined in two studies just published in medical journals.
But they represent the first reports of hospital outbreaks of bacteria containing the so-called NDM-1 enzyme in Canada. In each case, at least one of the people who carried the bacteria into the hospital seemed to have acquired it in Canada.
Previous NDM-1 cases in this country have been seen in individual cases and generally in people who had travelled outside Canada for health care – most commonly to India, but also on occasion to the United States.
“For many years the term superbug has been used and thrown around. And there have been threats that we’ll end up with a situation where there are infections that end up not being treatable because of the risk of drug resistance,” says Dr. Andrew Simor, senior author of one of the studies, which appeared in the journal Infection Control and Hospital Epidemiology.
“I think we’re actually seriously now approaching that point with these NDM-1s.”
The NDM-1 enzyme – the ND stands for New Delhi – was first found in 2008 in a Swedish person who had travelled to India for medical treatment. The discovery, reported in the journal Lancet, rang alarm bells the world over because it represented a new mechanism of drug resistance.
NDM-1 positive bacteria were first found in Canada in 2010.
Drug-resistant bacteria have been around as long as there have been antibiotics. And with increasing use of the drugs in the second half of the 20th century, the resistant bacteria flourished, leaving the pharmaceutical industry scrambling to try to stay ahead of the bugs.
But NDM-1 isn’t a bacterium. It’s an enzyme, produced by some bacteria, which disables an alarming array of antibiotics.
The few drugs that do treat NDM-1 positive bacteria are antibiotics that are rarely used. One, colistin, is highly toxic; doctors do not use it if they have an option. And NDM-1 positive bacteria become resistant to colistin over time, Simor says.
Perhaps more upsetting is the fact that the gene responsible for making the enzyme is promiscuous – it is able to move from one bacteria to another, conferring on each a level of drug resistance that leaves doctors with few treatment options.
One patient described in one of these studies had both E. coli and Klebsiella pneumoniae bacteria that contained NDM-1, leaving the authors to conclude the enzyme passed from one bug to the other in the patient.
Dr. Allison McGeer, the head of infection control at Toronto’s Mount Sinai Hospital, is an author of that paper, which appeared in the journal Clinical Infectious Diseases.
The article is the first describing a hospital outbreak involving NDM-1 organisms in Canada. It occurred at William Osler Health System in Brampton, northeast of Toronto, and was first spotted in October 2011.
“Everywhere you turn there is bad news,” McGeer says of NDM-1 and a handful of similar enzymes that confer resistance to drugs in the beta-lactam class of antibiotics.
The Brampton outbreak involved five patients, all carrying Klebsiella pneumoniae. Molecular study of the bacteria from all five showed they were linked. None of the patients in the outbreak had travelled to or been hospitalized in countries where NDM-1 is endemic.
The researchers who investigated the outbreak were not able to determine where the bacteria had been acquired.
Simor’s study describes an outbreak at Toronto’s Sunnybrook Health Sciences Centre, where he is head of microbiology. The outbreak was identified in January 2011 and was over by February 2012.
During that time two patients came into the hospital with different strains of NDM-1 Klebsiella pneumoniae. One had received previous health care in India, but the second had no history of travel to the Indian subcontinent.
From these two patients, the resistant bacteria spread to seven others.
Five of the nine were just carrying the bacteria. At the time of their hospitalization the bugs were not making the patients sick – other ailments were.
But four of the patients did develop infections caused by their NDM-1 positive bacteria; two had infections in their bloodstream and two had urinary tract infections.
Some of the patients who picked up the bugs were roommates of people carrying the bacteria, and others were on the same ward.
In one case, a patient moved into a room that had been occupied by one of the positive patients and then picked up the bacteria. An investigation pinpointed a handwashing sink in the room as the likely source of the bacteria. Health-care workers had used the sink to dispose of bath water and other fluids.
NDM-1 positive bacteria were growing in the biofilms in the sink’s pipes and repeated efforts to disinfect the sink failed. Eventually the sink and the sink traps were replaced.
McGeer, who has battled a sink-related outbreak – though not with a bacteria carrying NDM-1 – shudders at the idea.
“If we get our sinks contaminated with an NDM Kleb pneumo” – a short form for Klebsiella pneumoniae – “in our ICU, it will be unpleasant. Expensive.”
Simor’s study outlines the efforts Sunnybrook’s infection-control team took to stop transmission. Tracing contacts of all the patients was not easy, and in fact the majority of the contacts had been discharged before they could be tested to see if they were carrying the bug.
Typically infection-control teams would take a rectal swab of patients to see if they are carrying organisms and if they are, whether those organisms are NDM-1 positive.
But in some of the cases in the Sunnybrook outbreak, swabs were negative until about three weeks after exposure. Hospitals that didn’t test that far out might miss such cases.
Simor suggests with numbers of NDM-1 cases still low in Canadian hospitals, facilities may have a hard time deciding how much effort they should put into finding such cases at this point.
“So the question is how extensively do you do surveillance when there’s little bang for the buck? I think we’re going to have to be able to gear up our surveillance as the numbers increase. And I have no doubt they will increase.”
When asked if hospitals and public-health officials in Canada are paying enough attention to the threat, McGeer’s answer suggests she isn’t sure.
“People are paying attention to it. I am sure that we’re not paying enough attention to it to be really good at dealing with it. I’m hoping we’re paying enough attention to it to be okay.”
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