Wednesday, July 2, 2003
WHO has today removed Toronto, Canada, from its list of
areas with recent local transmission of SARS. The last probable case was
detected on 12 June and immediately isolated. When 20 days, or twice the
incubation period, have passed without detection of a new case, the chain
of human-to-human transmission is considered broken.
“This is a great achievement for public health in
what we hope is the final phase of the global emergency,” said David
Heymann, the WHO Executive Director for communicable diseases. “Toronto
faced an especially challenging outbreak. As we have learned, SARS is
a difficult disease that produces many surprises and setbacks.”
“We should all pay tribute to the health workers
and others in Canada who had their lives disrupted and threatened by this
disease. When the virus returned to start a second outbreak, health workers
continued the fight and have now won it. We also need to remember the
commitment of Canada’s scientists, who rapidly provided information
about the virus and its epidemiology that has benefited public health
around the world.”
Toronto was among the first areas affected after the virus
moved out of southern China, in late February, and began to spread internationally.
WHO advised travellers to avoid all but essential travel to Toronto on
23 April. The advice was lifted a week later. On 14 May, Toronto was removed
from the list of areas with recent local transmission, only to return
on 26 May after the virus surfaced in a second outbreak.
All of the earliest and most severe SARS outbreaks have
been traced to contact with an infected medical doctor from Guangdong
Province, China, who spent a single night (21 February) on the 9th floor
of the Metropole Hotel in Hong Kong. At least 16 guests and visitors to
the same floor became infected. One has been identified as the source
case, at the Princes of Wales Hospital, for the Hong Kong outbreak. Others,
who carried the virus with them when they returned home, seeded outbreaks
in Toronto, Viet Nam, and Singapore.
The mechanisms by which the virus spread from one infected
person to so many guests and visitors are still not fully understood.
No hotel staff were infected.
Another mystery is why the SARS virus spreads more efficiently
in sophisticated hospital settings – another factor that may have
contributed to the severity of Toronto’s outbreak. Both epidemiological
and anecdotal evidence suggests that certain procedures, such as difficult
intubation and use of nebulizers, that are more common in sophisticated
hospitals also increase the risk of infection.
When the outbreak began in Toronto and, simultaneously,
at the other initial sites, no one was yet aware that a new disease, capable
of rapid spread within hospitals, had surfaced in China. Hospital staff,
struggling to save lives, were unaware of the need to protect themselves.
As a result, the SARS virus spread rapidly within hospitals and then out
into the wider community as other patients, hospital visitors, and close
contacts of staff became infected.
After WHO issued the first global alert to SARS, on 12
March, all countries experiencing imported cases, with the notable exception
of Taiwan, have been able to either prevent any further cases or keep
the number of additional cases very small.
With today’s change in the status of Toronto, Taiwan
now remains the last area in the world to have experienced recent local
transmission of SARS.
Friday, June 13, 2003 the category of pattern of SARS
transmission for the city of Toronto has been changed from “B”
to “C”. This is because a probable case with laboratory confirmation
of SARS coronavirus exported from Toronto had not been previously identified
as a contact and put into voluntary home isolation. “Pattern B”
transmission is defined as an area having more than one generation of
local probable SARS cases, but only among persons who have been previously
identified and followed-up as known contacts of probable SARS cases. “Pattern
C” transmission is defined as an area having local probable cases
occurring among persons who have not been previously identified as known
contacts of probable SARS cases.
Thursday, June 12, 2003 global media reports of apparently
one possible case of SARS has been verified as exported from Toronto to
the US. Notably there are concerns that Canadian HCWs apparently failed
to notify US authorities of the possibility.
The World Health Organization (WHO) has added Toronto,
Canada (May 26, 2003) to the list of areas with recent local transmission
of SARS. The change in status follows information, communicated by Health
Canada, about new clusters of 26 suspect and 8 probable cases of SARS
linked to 4 Toronto hospitals. Notably Health Canada has released a document
revised on May 30, 2003 with new SARS case definition guidelines.
Apparently an urgent alert was sent on May 23,
2003 to all health and long-term care facilities and service providers
in Toronto. Potential exposures may include staff, patients, visitors
and related contacts. Notably the SARS virus contamination may also have
spread from the Toronto area to hospitals in Ottawa (June 2, 2003). Procedures
are apparently in place for exit screening the thermal emissions of
all travellers leaving the Toronto area.
As a precautionary measure, apparently all cases
are being treated as possibly representing SARS virus contamination until
proven otherwise. Actions being taken include immediate isolation of all
possible cases, heightened infection control, intensive contact tracing,
and voluntary or enforced home quarantine of identified contacts. These
measures have proved reasonably effective in quickly containing outbreaks.
Apparently over 7000 possible cases were in quarantine effective
May 30, 2003 as a preliminary countermeasure. Notably global media
reports (BBC June 1 , 2003) indicate numerous quarantine cases in Toronto
have been ignoring quarantine orders.
Although the results of laboratory and
epidemiological investigations are pending, apparently sufficient information
is available to determine that the index, or first, case in the present
outbreak has transmitted infection to others in more than one generation
of local transmission. Toronto is therefore classified as having “pattern
B” transmission. This is defined as more than one generation of
local probable SARS cases.
Significantly on June 11, 2003 the World
Health Organization is deeply concerned by the resurgence of SARS
cases in Toronto, reported to WHO on 22 May, and is following the
situation closely. Toronto, which had been removed from the list of
areas with recent local transmission on 14 May, was again added to the
list on 26 May following evidence that more than one generation of new
cases had occurred. Since the disease first resurged in Toronto, over
90 new probable cases have been reported.
Health authorities in Toronto are again
on high alert, and are treating all hospital-associated clusters of
patients with fever or respiratory symptoms as possible SARS cases until
proven otherwise. Possible cases are immediately isolated. All contacts
are being traced and, when warranted, placed in home quarantine. Infection
control measures are being followed in all affected facilities. WHO
welcomes these precautionary measures.
Canadian authorities have most recently
reported a possible cluster of SARS patients in a hospital east of Toronto.
Although no clear epidemiological link has been established that could
explain this new cluster, officials have adopted a cautious approach.
Over the last 3 days, 15 dialysis patients at the Lakeridge Health Centre
in Whitby exhibited respiratory and febrile illnesses. After clinical
review and laboratory investigations to detect other causative agents,
around half of these patients have now been excluded from consideration
as possible SARS cases. The remaining patients are being closely monitored.
These are other investigations are ongoing
and many questions remain to be answered before firm conclusions
can be reached.
WHO is also awaiting further information
on cases in other countries that may have been exported from Toronto.
WHO is not yet convinced that such cases have been conclusively documented.
One of the most dangerous stages in the
evolution of any outbreak, and most especially one caused by a new and
poorly understood disease, occurs when cases begin to decline and previous
levels of high alert and precautionary measures likewise begin to level
off. Much about the clinical behaviour of SARS and its mode of transmission
requires further research. Until knowledge improves, precautionary measures
such as those being followed in Toronto are the best approach from a
public health perspective.
