The Role of Surveillance in Major Outbreaks
It seems incredible that a disease as devastating as AIDS could have spread silently to many countries over many years before it was detected and before effective control measures were implemented in the 1980s. In recent years, surveillance and response systems at all levels have been more effective at identifying and preventing spread of infectious diseases.
Example: Surveillance and Global Response to SARS
An epidemic of severe pneumonia of unknown etiology was detected in Guangdong province, China, in November 2002, and control measures were instituted on the basis of the way the disease spread from person to person. In February and March 2003, the disease spread to Hong Kong (China) and then to Vietnam, Singapore, Canada, and elsewhere (WHO 2003b). This new disease was named severe acute respiratory syndrome, and a preliminary case definition was established on the basis of initial epidemiologic investigations. A novel coronavirus (SARS-CoV) was identified as the causative agent in March, and mapping of the full genome was completed in April. This global pandemic ended in July 2003, as transmission was interrupted in Taiwan (China), after more than 8,000 patients in 26 countries and five continents were affected and 774 deaths were confirmed (Peiris and others 2003).
WHO spearheaded the global effort to control this pandemic, working with national and subnational health workers. In China, the FETP, which was initiated in October 2001 in the China Center for Disease Control, mobilized all 20 of its trainees, and they contributed substantially to the surveillance, investigation, and control of the SARS outbreak, working with local health officials (CDC 2003a). In Canada, which had the most cases of SARS outside Asia, 8 of the 10 FETP residents were involved in the SARS outbreak. They instituted surveillance, conducted epidemiologic investigations, designed prevention and control guidelines, responded to inquiries from the media and the public, and planned and implemented epidemiologic studies (http://www.phac-aspc.gc.ca/cfep-pcet/outbreaks_e.html).
The success of this global effort to control the first new epidemic disease of the 21st century depended on a combination of open collaboration among scientists and politicians of many countries and the rapid and accurate communication of surveillance data within and among countries. Rapid global spread was recognized, and a global surveillance network was established on the basis of an agreed-upon case definition that was sufficiently specific to ensure effective reporting.
Public health surveillance is critical to recognizing new cases of SARS and differentiating this disease from other causes of severe respiratory illness, especially influenza (Heymann and Rodier 2004). Ongoing research into sources in the environment as well as clinical, laboratory, and epidemiologic concerns will improve surveillance for this critical public health problem. Notably, this highly contagious disease—for which there is neither a vaccine nor a cure—was controlled by competent, dedicated health workers with access to excellent communications. SARS presented a greater challenge than smallpox, for which long incubation periods and vaccine facilitate control (Mack 2005). Although it is reassuring that national, regional, and global systems were effective in controlling SARS, there is no reason to rest on our laurels. The only certainty is that there will be more new challenges, very possibly including further outbreaks of SARS.
Example: Avian Influenza in Thailand
The disastrous pandemic (worldwide epidemic) of influenza in 1918 is thought to have originated from epidemics in birds, as were the influenza pandemics of 1957 and 1968 (Ungchusak and others 2005). In early 2004, large epidemics of avian influenza were recognized in birds in eight Asian countries; by November, the disease had spread from birds to 44 humans, 73 percent of whom died (Ungchusak and others 2005). This contagion sparked fears that the highly lethal avian virus might be adapting to spread from person to person, which could cause extensive health and economic damage around the world. In Thailand, avian influenza was investigated by FETP graduates and others in the Thai Ministry of Health in partnership with CDC. By applying field epidemiologic techniques supported by laboratory studies, they detected that the virus was being spread from human to human in a family. It is likely that person-to-person transmission may have occurred in other countries, where field epidemiology was not used.
The Thai example is important for achieving the following: (a) raising global awareness of the potential of a global catastrophe early enough that plans can be made to avert or decrease harm and (b) demonstrating that, as with SARS, the disease could be controlled with proven field epidemiologic methods supplemented by good communications, without vaccines, drugs, or a high-technology laboratory or surveillance system (Mack 2005).
Example: Ebola in Uganda, the Role of the PHSWOW
On October 8, 2000, a second-year student in the Ugandan PHSWOW returned to Gulu district in northern Uganda for his field project. He found a hospital jammed with patients with high fevers, diarrhea, and bleeding. He diagnosed viral hemorrhagic fever. He called the Ministry of Health in Kampala, where that weekend a graduate of the PHSWOW was in charge of taking calls about epidemics. She agreed with his diagnosis and arranged for samples to be rushed to the National Institute for Virology in South Africa, the nearest WHO reference center for viral hemorrhagic fevers. When the minister of health arrived at his office the next day, the graduate briefed him. Recognizing the gravity of the situation, the minister sent the graduate to head the public health team surveillance and control team in Gulu, and the student headed the clinical team that established infection control in hospitals and treated patients.
Laboratory tests quickly confirmed that the illness was Ebola hemorrhagic fever, which usually kills more than 50 percent of those infected (Heymann 2004). Public health surveillance was difficult for several reasons. Because the disease was severe and rapidly fatal, rural villagers feared that they might be stigmatized if the government knew about cases in their area. Some sought out traditional healers; others fled as soon as they realized they had been exposed, which prompted outbreaks in two other districts. Gulu was a politically unstable area, and some villages were difficult to reach because of rebel or bandit activity. The Ugandan government mobilized its military to help with case finding and invited WHO, CDC, and other international teams to assist. Patients with Ebola infection require intense nursing and medical attention to control bleeding, diarrhea, and fevers. Some patients bleed easily, and all their secretions can be highly infectious. Hospitals in Gulu were desperately short of supplies to control the spread of infection from so many patients simultaneously. In spite of this situation, Ugandan health workers selflessly cared for the sick. By January 23, 2001, a total of 425 cases had occurred, the largest Ebola outbreak recorded. Only 53 percent of the patients had died, a proportion far less than the 88 percent reported in the 1976 Ebola outbreak in the Democratic Republic of Congo (formerly Zaire) and other previous epidemics (WHO Report of an International Commission 1978). Sadly, 22 health care workers were infected. Because the team from the Ugandan Ministry of Health set up active surveillance nationwide, the other two outbreaks, started when infected Gulu residents fled to distant villages, were quickly detected and controlled. International observers commented, "National notification and surveillance efforts led to the rapid identification of these foci and to effective containment" (CDC 2001).
The Ugandan Ministry of Health invested in developing competent, motivated health workers through the PHSWOW, an active partnership with Makerere University, the Rockefeller Foundation, CDC, and WHO. Both students and graduates contributed to the ministry's ability to rapidly identify and control this dangerous epidemic. Because the minister had timely evidence, he was able to notify other countries quickly and to bring in international teams before the disease spread further. Partially because of the lessons learned from this epidemic, Uganda has become one of the leading countries in implementing the IDSR program.
