David L. Heymann
Executive Director, Communicable
Diseases, World Health Organization, Geneva, Switzerland
The international response to the severe acute respiratory syndrome (SARS) outbreak,
from
March to July 2003, tested the assumption that a new and emerging
infection–one that had not yet demonstrated its full epidemiologic potential
but was spreading from person to person and continent to continent–could be
prevented from becoming endemic. Within 4 months after the first global alert about
the
new disease, all known chains of transmission had been interrupted in an outbreak
that
affected 27 countries on all continents. Most public health experts and scientists
believe that the question of whether SARS has become endemic can only be answered
after
at least 12 months of postoutbreak surveillance. The SARS experience, however, made
one
lesson clear early in its course: inadequate surveillance and response capacity in
a
single country can endanger national populations and the public health security of
the
entire world. As long as national capacities are weak, international mechanisms for
outbreak alert and response will be needed as a global safety net that protects other
countries when one nation’s surveillance and response systems fail.
During the last decade of the 20th century, several outbreaks, including cholera in
Latin
America, pneumonic plague in India, and Ebola hemorrhagic fever in the Democratic
Republic of the Congo, caused great international concern (
1
–
3
). These events demonstrated the consequences that delayed national recognition
and response to outbreaks could have: illness and death of national populations
including health workers, potential spread to other countries, and significant
disruptions of travel and trade. These outbreaks also emphasized the need for a global
surveillance and response mechanism. The Global Outbreak Alert and Response Network
(GOARN), set up in 1997 and formalized in 2000, was one major response to this need
(World Health Organization [WHO], unpub. data and
4
). Though the network, which now has 120 partners throughout the world, currently
identifies and responds to more than 50 outbreaks in developing countries each year,
the
SARS outbreak was the first time that GOARN identified and responded to an outbreak
that
was rapidly spreading internationally.
One of the partners in GOARN is the WHO Global Influenza Surveillance Network, which
was
established in 1947 to guide the annual composition of vaccines and provide an early
alert to variants that might signal the start of a pandemic of rapidly evolving
influenza viruses. This network was placed on alert in late November, when the Canadian
Global Public Health Intelligence Network (GPHIN), also a partner in GOARN, picked
up
media reports of an influenza outbreak in mainland China (
5
). Simultaneously, another GOARN partner, the U.S. Global Emerging Infections
Surveillance and Response System (GEIS), became aware of similar reports about a severe
outbreak, with influenza B the suspected cause, in Beijing and Guangzhou. As GOARN
continued to receive reports about influenza outbreaks in China, WHO requested
information from Chinese authorities on December 5 and 11. On December 12, WHO received
a detailed report on data collected at Chinese influenza surveillance sites, indicating
that investigation of 23 influenza virus isolates had confirmed type B strains in
all
but one and that the number of cases was consistent with the seasonal pattern in
previous years. The information was reassuring and an indication that the influenza
surveillance system was working well.
Although information is incomplete, retrospective case identification by Chinese and
GOARN epidemiologists since May 2003 suggests that two respiratory disease outbreaks
occurred in Guangdong Province in late November 2002: influenza and what now appears
to
have been a first wave of SARS cases—an atypical pneumonia that was
characterized by small, seemingly unrelated clusters of cases scattered over several
municipalities in Guangdong, with low-level transmission to healthcare workers (
6
). This first wave of atypical pneumonia appears to have continued until a second
wave of disease with amplified transmission to health workers began occurring during
the
first 10 days of February (WHO, unpub. data). On February 10, 2003, the WHO office
in
Beijing received an email message describing an infectious disease in Guangdong Province
said to have caused more than 100 deaths. On February 11, the Guangzhou Bureau of
Health
reported to the press more than 100 cases of an infectious atypical pneumonia outbreak
that had been spreading in the city for more than 1 month. That same day, the Chinese
Ministry of Health officially reported to WHO 300 cases and 5 deaths in an outbreak
of
acute respiratory syndrome, and the next day reported that the outbreak dated back
to
November 16, 2002, that influenza virus had not yet been isolated, and that the outbreak
was coming under control (
7
).
When the reports of a severe respiratory disease were received by WHO on February
11,
2003, a new strain of influenza virus was the most feared potential cause, and the
WHO
Global Influenza Network was again alerted. Concern grew on February 20, when the
network received reports from Hong Kong authorities confirming the detection of A(H5N1)
avian influenza virus in two persons, and WHO activated its influenza pandemic
preparedness plans (
8
).
During that same week, laboratories of the WHO Global Influenza Surveillance Network
began analyzing specimens from a patient with severe atypical pneumonia hospitalized
in
Hanoi after travel to Hong Kong. Concurrently, GOARN response teams in Vietnam and
Hong
Kong began collecting clinical and epidemiologic information about the patient and
a
growing number of others with similar symptoms. As more specimens entered the network
laboratories, influenza viruses were ruled out as the causative agent. WHO made its
first global alert on March 12, followed by a second, on March 15, when more than
150
suspected new cases had been reported from several geographic areas, including Hong
Kong, Singapore, Vietnam and Canada (
9
,
10
). With the second alert, WHO provided a case definition and name, thus beginning
a coordinated global outbreak response that brought heightened vigilance everywhere
and
intense control efforts. GOARN linked some of the world’s best laboratory
scientists, clinicians, and epidemiologists electronically, in virtual networks that
provided rapid knowledge about the causative agent, mode of transmission, and other
epidemiologic features (
11
). This real-time information made it possible for WHO to provide specific
guidance to health workers on clinical management and protective measures to prevent
further nosocomial spread. It also made possible recommendations to international
travelers to curtail international spread. Recommendations were at first nonspecific,
urging international travelers to have a high level of suspicion if they had traveled
to
or from areas where the outbreak was occurring. But as more information became
available, airports were asked to screen passengers for history of contact with SARS
and
for persons with current illness that fit the SARS case definition. Finally, when
these
recommendations did not completely stop international spread, passengers themselves
were
asked to avoid travel to areas where contact tracing was unable to link all cases
to
known chains of transmission (
12
). Within 4 months, transmission of SARS had been interrupted at all sites, and
on July 5, 2003, the SARS outbreak was declared contained (
13
).
As many times occurs with emerging and reemerging infectious diseases, national
surveillance mechanisms failed to identify and respond to the emerging outbreak of
SARS
early enough to prevent its toll of sickness, death, and international spread (
14
). In May 2003, ministers of health from the 192 member countries of WHO
expressed their deep concern about the impact of SARS and its implications for future
outbreaks, which were considered inevitable. In two resolutions, they called for
increased national capacity development for surveillance and response and endorsed
the
ways in which GOARN obtained information about SARS and supported containment efforts
(
15
,
16
). The resolutions stressed the need for countries to give more attention, with
WHO support, to the strengthening of national surveillance and response capacity,
and
encouraged WHO to continue to strengthen GOARN, its safety net for global alert and
response. As SARS so amply demonstrated, protection against the threat of emerging
and
epidemic-prone diseases requires strong defense systems at national as well as
international levels.