Study Population

Guangdong Province has a population of 85.2 million, including 9.9 million in Guangzhou city (7). All public health and most hospital services are under the direction of the Health Bureau of Guangdong Provincial People’s Government. The public health function is performed by one provincial Center for Disease Control and several municipal centers, together with a network of district and county centers, each responsible for a population of 500,000–1 million. Nearly all hospitals are operated by the public sector, but patients are charged for medical treatment. Primary health care in the province is rudimentary, and most patients report directly to hospital emergency rooms.

Data Sources

We analyzed data from two sources: the Guangdong surveillance database and a case investigations database. We also interviewed staff from the Guangdong Provincial Centers for Disease Control, and Foshan Municipal Center for Disease Control to obtain supplementary information on early-onset cases. Information on early cases in the neighboring Guangxi Province was obtained from local investigators by a visiting WHO team, led by one of the authors (CKL). Early cases were defined as those with a date of onset from November 1, 2002, to January 31, 2003, and late cases as those with a date of onset from February 1 to April 30, 2003. Population denominators were obtained from the Guangdong provincial census for 2000 (7).

Surveillance Database

Guangdong Provincial Center for Disease Control coordinated the surveillance database. Early cases were identified during the course of case investigations or after voluntary reporting by clinicians. Such cases were only included in the database if they conformed to the case definition subsequently adopted for surveillance. Since early February 2003, hospitals at all levels in the health system were required to report cases of atypical pneumonia (probable SARS) immediately by telephone to the local center for disease control, which then forwarded reports electronically to the provincial center on the same day. The diagnostic criteria for reporting were: 1) having close contact with a patient or having infected other people, 2) fever (>38°C) and symptoms of respiratory illness, 3) leukocyte count <10.0 x 10⁹/L, 4) radiographic evidence of infiltrates consistent with pneumonia or respiratory distress syndrome on chest x-ray, and 5) no response to antimicrobial drug treatment (within 72 hours). Patients were considered to be probable SARS patients if they meet criteria 1–4 or 2–5 but were excluded if an alternative diagnosis could fully explain their illness. The dataset contains patient demographics, including occupation; dates of onset, admission and report; criteria required for the case definition; and details of laboratory specimens that were collected.

Case Investigation Database

Contact tracing staff at the district center level administered a standard questionnaire to all case-patients within 24 hours of reporting. These data form the basis of the case investigation database and comprise patient demographics; clinical features on admission to hospital; contact history (living with, working with, caring for, or visiting the home of a patient) and name, age, and address details of contacts; and exposure risk factors for community cases (non-healthcare workers), including travel history, hospital visits, animal contact, and living conditions. Patients not employed as healthcare workers were classified as community case-patients. Comparisons were made between features of early-onset and late-onset community cases, and primary (no contact history) and secondary community cases. Extra information was collected on early patients by means of informal interviews with center staff, which focused on index patients in each of the seven municipalities initially affected. Data were particularly sought on occupational history and contact networks, and a detailed case series was compiled.

Data Analysis

Data were entered into Excel databases (Microsoft, Redmond, WA). Descriptive analyses were carried out using EpiInfo version 6 (Centers for Disease Control, Atlanta, GA) and SPSS version 10.0 (SPSS Inc., Chicago, IL). The surveillance database was used for analysis by age, sex, occupation, and clinical signs and symptoms. The case investigation database was used for comparing early- and late-onset cases and cases with or without a contact history. Incidence rates were calculated for November 2002 to April 2003. For comparisons of signs and symptoms by age, younger adults were used as the reference group for both children and older persons. Chi-square test or, when appropriate, Fisher exact test was used for comparison of proportions, Mann-Whitney test for comparison of continuous variables, and chi-square test for linear trend for analysis of time trends. We report maximum likelihood estimates for odds ratios (OR) with exact 95% mid-p confidence intervals (CI) and consider p<0.05 to be significant.

Surveillance Database

A total of 1,454 SARS cases were reported in Guangdong Province from November 16, 2002, through April 30, 2003, including 55 deaths, a crude case-fatality rate of 3.8% for all ages, and 12.7% in people >65 years. Two children died: a 4-year-old, previously healthy girl with lobar pneumonia of unknown cause and a 10-year-old boy with recent acute hepatitis B.

Figure 1

Figure 1. Epidemic curve of cases of severe acute respiratory syndrome by date of onset, November 1, 2002–April 30, 2003, in Guangdong Province, China, showing cases in the community and in healthcare workers....

Figure 2

Figure 2. Geographic distribution of population in: (A) urban districts of Guangzhou city, (B) Guangdong Province and district-specific incidence of severe acute respiratory syndrome (per 100,000 population).

Figure 3

Figure 3. Timeline of cases of severe acute respiratory syndrome by week of onset, November 1, 2002–April 30, 2003, in the nine predominantly affected municipalities of Guangdong Province, China.

The initial phase of the epidemic, November–late January, was characterized by sporadic cases followed by a sharp rise in late January and a sharp decline in the first half of February, and thereafter a gradual decline (Figure 1). The epidemic peak occurred at the end of the first week of February with approximately 55 new cases each day. Cases occurred in 15 municipalities in the province but were concentrated in the Pearl River delta area (Figure 2A), and confined almost exclusively to urban areas, particularly the seven municipalities of Foshan, Guangzhou, Heyuan, Jiangmen, Shenzhen, Zhongshan, and Zhaouqing (located 20–130 km from Guangzhou). The highest incidence occurred in Guangzhou city (12.5 cases per 100,000 people) (Figure 2B), and outbreaks appear to have occurred in different municipalities at varying stages of the epidemic (Figure 3).

Figure 4

Figure 4. Number of patients with severe acute respiratory syndrome by age, and age-specific incidence (per 10,000 population), November 1, 2002–April 30, 2003, Guangdong Province, China.

Median age of patients was 35.0 years (range 0–92 years), and the highest age-specific incidence was in persons 65–69 years (3.2 per 100,000 people) (Figure 4); 53.2% of cases were female. Five deaths occurred among 343 cases in healthcare workers (24% of 1,429 cases for whom occupation is known); 75.1% of healthcare worker cases were in women. The proportion of healthcare worker patients was highest in the early phase of the epidemic (32% with date of onset in January 2003) and declined as the epidemic progressed (27% in February, 18% in March, and 17% in April) (Table 1). Throughout the epidemic, a high proportion of community case-patients did not report contact history, ranging from 58% in February to 74% in April. This proportion was even higher in children (91% in those <5 years, 81% in those 5–14 years) and in persons >65 years (82%).

Analysis of occupation status, excluding healthcare workers and case-patients with known exposure, shows that the proportion of cases in students (0% in January 2003 or before; 7% in February; 14% in March; 18% in April, p < 0.001) and housewives (0% in January 2003 or before; 5% in February; 14% in March; 15% in April, p < 0.001) increased as the epidemic progressed (Table 2). A high proportion (9/23, 39%) of early cases were food handlers (this category includes persons who handle, kill, and sell food animals, as well as those who prepare and serve food), but none were farmers handling livestock or poultry. Of the nine early cases in food handlers, seven were restaurant chefs working in township restaurants (where a variety of animals were slaughtered on the premises), one was a market produce buyer for a restaurant, and one was a snake seller in a produce market (where a variety of live animals were offered for sale). Six of the food handlers lived or worked in Shunde (1.7 million population), an urban district of Foshan municipality, though none could be directly linked to each other through contact history.

Case Investigation Database

Detailed data from case investigation interviews were available for 662 (45%) of 1,454 patients. Median age was 31.0 years (range 0–86 years), 56% were female, and 44% were male. The signs and symptoms in adults (18–64 years) were compared with those in children (<18 years) and older persons (>65 years) (Tables 3 and 4). Children were more likely to have a runny nose and dry cough on physical examination but less likely to have chills, malaise, headache, muscle aches, or difficulty breathing. Older persons were more likely to report having sputum and to have a dry or productive cough on physical examination but less likely to complain of chills, malaise, or sore throat. Nearly all patients had a high body temperature (median 39.0°C, range 36.8–42.0°C) lasting in most patients for 1 to 4 days (median 4.0 days; range 1–9 days). Median leukocyte count was 5.8 x 10⁹/L (range 1.0–63.4 x 10⁹/L), and 13.9% of patients had leukopenia (<3.5 x 10⁹/L). Older persons had a higher median leukocyte count than younger adults (6.6 x 10⁹/L for those >65 years, 5.6 x 10⁹/L for those 18–64 years, p = 0.056), and fewer had leukopenia.

Comparison of case categories indicate that community case-patients with a contact history were more likely to have visited a hospital in the previous 2 weeks than patients without a contact history (OR 6.83, 95% CI 2.89 to 16.73) (Table 5). Patients without a contact history were no more likely to report a history of travel or animal contact. Early-onset patients were more likely to live within walking distance of a produce market (an agricultural market where live animals are sold, killed, and butchered in situ, also known as a “wet market”) than late-onset patients (OR undefined, lower 95% CI 2.39). Living near a poultry or livestock farm or having other types of animal contact, including domestic pets or livestock, poultry, or specific wild animals or birds, was not associated with a high risk for SARS.

Case Series of Index Patients

The index patients in each of the seven earliest affected municipalities all had a date of onset before January 31, 2003 (Table 6). In five municipalities (Foshan, Jiangmen, Zhongshan, Guangzhou, Shenzhen), outbreaks appear to have occurred independently, but the outbreak in Heyuan may be linked to that in Shenzhen and the outbreak in Zhaoqing to that in Guangzhou. Index patients from the eight other municipalities involved in the epidemic had a date of onset after March 1, 2003, and a travel history to an affected area, so these were excluded from the analysis.

Patient 1 had the earliest case, identified by retrospective case searching. He lived with his wife and four children in Foshan city and became ill on November 16, 2002. He had not traveled outside Foshan in the 2 weeks before his illness and had no contact history, but he had prepared food including chicken, domestic cat, and snake. He was part of a cluster of five patients, including his wife (42 years old, onset December 1), a 50-year-old aunt who visited him in the hospital on November 20 (onset November 27), and the aunt’s 50-year-old husband (onset November 30) and 22-year-old daughter (onset December 4) ( Appendix, Cluster A). None of patient l’s four children were ill. Subsequent clusters in Foshan included a food handler who infected a family member and two healthcare workers (Appendix, Cluster B) and a food handler who infected several healthcare workers (Appendix, Cluster C).

Patient 2 lived in Heyuan but worked as a restaurant chef in Shenzhen. His work was mainly stir-frying and did not involve killing animals. His animal contact history is unknown. He returned to Heyuan after becoming ill, was admitted to the local hospital and transferred to Guangzhou 2 days later. He infected a work colleague (41-year-old man, onset December 16), six healthcare workers in Heyuan (onset December 24–28), and a physician who accompanied him in the ambulance from Heyuan to Guangzhou (28-year-old man, onset December 25). Patient 3, from Jiangmen, had no contact history, no history of animal contact, and no known forward transmission. Patient 4 worked as a chef in a Zhongshan township restaurant, where he prepared steamed dishes and had contact with snakes, civet cats, foxes, and rats. He infected his 30-year-old wife (onset January 3), a 39-year-old male friend who visited him in the hospital (onset January 5), and a physician (35-year-old man, onset January 4). Patient 4 was one of two patients responsible for infecting at least three healthcare workers (onset January 4–7). Patient 5, from Guangzhou, had no history of animal contact other than with a pet guinea pig that died a month before his symptoms began. He infected a hospital intern (onset January 14) and six other healthcare workers (onset January 14–22) at Guangdong Traditional Chinese Medicine Hospital. Patient 6, from Shenzhen, had visited Hong Kong on January 14, the day before symptom onset. However, he had no contact history or contact with animals. He infected a work colleague (43-year-old man, onset January 29) and died 14 days after becoming ill. Patient 7, from Zhaoqing, was the only female index case. She traveled to Guangzhou 2 weeks before becoming ill, although she could not recollect contact with anyone with symptoms of SARS. She worked at a market but did not sell animals. She infected her 16-year-old son (onset February 3) and a physician (25-year-old woman, onset January 31).

The index patient in the neighboring province of Guangxi was a 26-year-old man, who infected several family members. He worked as a driver for a wild animal dealer and returned home to Guangxi after becoming ill on January 8, 2003. The dealer supplied Guangdong markets with wild animals from Guangxi, other Chinese provinces, and Vietnam.