Quarantine Methods and Prevention of Secondary Outbreak of Pandemic (H1N1) 2009

Quarantine Methods and Secondary Outbreak Prevention


P andemic (H1N1) 2009 infl uenza emerged in Mexico in
March 2009 and by June 10 had rapidly spread to 74 countries (1,2). Nonpharmaceutical interventions for pandemic infl uenza at the community level were recommended by the World Health Organization before and during the pandemic (3,4). One such nonpharmaceutical intervention was quarantine of contacts of persons with confi rmed cases. A key question in closed settings (e.g., military barracks) was how to prevent a secondary outbreak of infl uenza among those quarantined.
The fi rst identifi ed case of pandemic (H1N1) 2009 in mainland People's Republic of China was imported from the United States and reported on May 11, 2009 (5). On May 29, the Chinese Ministry of Health required that each confi rmed case-patient and each contact be isolated and quarantined in 1 separate room to contain transmission of the virus (6). Containment efforts appeared to successfully prevent community spread until mid-August (7). The Chinese Ministry of Health adjusted the quarantine guidelines on August 20 and permitted incomplete quarantine of contacts (e.g., quarantining >1 contact in 1 room) (8). We conducted an observational study of a pandemic (H1N1) 2009 outbreak among students of a university in northern China in September 2009. Our goal was to compare the effectiveness of different quarantine methods for preventing a secondary outbreak among the persons in quarantine.

The Study
During August 31-September 12, 2009, an outbreak of pandemic (H1N1) 2009 occurred among students of a university in northern China. On August 31, pandemic (H1N1) 2009 was laboratory confi rmed in 6 students who had fever and acute upper respiratory symptoms. A subsequent investigation found that all of the confi rmed case-patients, along with 27 other students, had traveled by train from Shanghai to the university on the afternoon of August 28. One of the students (the index case-patient) had a cough during the trip on August 27. Another 5 students also had fever and infl uenza-like symptoms and visited the school medical services for treatment during August 28-30. When the outbreak was identifi ed, a total of 202 contacts (average age 21 years, range 19-23 years) were traced and immediately quarantined in a separate dormitory on September 1. Eighty-nine rooms (each with 1 toilet) and 9 apartments (each with 2 bedrooms and 1 toilet) were occupied. One or 2 contacts were assigned to each bedroom. Other control measures, such as ventilating and disinfecting each room, wearing masks, and washing hands, were strictly implemented in accordance with guidance provided by the Chinese Ministry of Health (8).
Oropharyngeal swabs from all contacts were collected and tested on the fi rst day of quarantine (September 1). Virologic laboratory testing subsequently indicated that 39 contacts were positive for pandemic (H1N1) 2009. Among the 163 virus-negative contacts, 11 had fever (>38°C) or infl uenza-like symptoms at the beginning of the quarantine; the other 152 had no fever or infl uenza-like symptoms on September 1.
Among the 152 virus-negative contacts who had fever or infl uenza-like symptoms, 20 were exposed to a viruspositive contact during quarantine; 19 shared a bedroom and a toilet with a virus-positive contact; and 1 shared a toilet but not a bedroom with a virus-positive contact. The other 132 were not exposed to any virus-positive contacts during quarantine, including 6 persons housed in single rooms and 126 sharing double rooms.
The temperature and symptoms of contacts were recorded 3× per day (8:00 AM, 2:00 PM, and 6:00 PM). We defi ned a suspected case as a virus-negative contact with sudden onset of fever >38°C and at least 1 of the following symptoms: cough, sore throat, runny nose, shortness of breath, headache, body aches, fatigue, vomiting or diarrhea, and absence of other diagnoses. Students with suspected pandemic (H1N1) 2009 infection who had high fever (>38.5°C) or severe respiratory symptoms (bad cough or dyspnea) were transferred to hospital for treatment; others who had fever <38.5°C or mild infl uenza-like symptoms were treated in the quarantine building. Because of a short-age of resources, laboratory testing of suspected case-patients in quarantine was not performed after the fi rst day.
Data were analyzed by using SPSS 15.0 (SPSS Inc., Chicago, IL, USA). χ 2 test and Fisher exact test were used to compare the attack rates of suspected cases between the groups under different quarantine arrangements. A p value <0.05 was considered signifi cant.
During the quarantine, 14 suspected cases were identifi ed among 152 virus-negative contacts, but none had high fever (>38.5°C) or severe respiratory symptoms. Of 19 initially virus-negative contacts sharing a room with a virus-positive contact, 5 suspected cases were identifi ed; onset of symptoms occurred during September 2-8. Also, of 126 initially virus-negative contacts who shared a room with a virus-negative contact, 9 suspected cases were identifi ed; onset of symptoms occurred during September 2-7 (Table, Figure). The attack rate of suspected cases differed signifi cantly between the 2 groups (p = 0.02, 2-tailed Fisher exact test).
Among 132 initially virus-negative contacts, who were not exposed to a virus-positive contact during the quarantine, no suspected cases were identifi ed among the 6 students in single rooms, but 9 students with suspected infection were identifi ed among 126 students in double rooms; onset of symptoms occurred during September 2-7 (Table; Figure). Attack rates for suspected cases between the virus-negative contacts in single rooms and those in double rooms did not differ signifi cantly (p = 1.00, 2-tailed Fisher exact test). All students with suspected infection had normal temperature with no infl uenza-like symptoms after September 9, and all quarantined persons were released by September 12.

Conclusions
In our study, the attack rate of suspected cases among pandemic (H1N1) 2009 virus-negative contacts increased signifi cantly when persons were quarantined in the same room or used the same bathroom as a virus-positive contact (p = 0.02, 2-tailed Fisher exact test). Nevertheless, quarantining each virus-negative contact in 1 room did not sig-nifi cantly decrease the attack rate of suspected cases among virus-negative contacts in comparison with quarantining 2 persons in 1 room. Our results support the effectiveness of quarantine in preventing a secondary outbreak of pandemic (H1N1) 2009 among contacts of confi rmed cases. Our results also support quarantining 2 virus-negative contacts in 1 room in situations where a large number of contacts have been traced but space is limited. Whether our fi ndings support quarantining >2 contacts in 1 room deserves further study.
During the quarantine, every room was routinely disinfected by university staff 1 × per day. Compliance of all contacts with regulations governing personal protection and hygiene was good. Also, staff were assigned to supervise the behavior of contacts in quarantine. These control measures did not contribute to the differences of the attack rate of suspected cases between the different cohorts in this study.
Our study is limited in that virologic laboratory confi rmation of suspected cases was not available. However, no other respiratory infections were known to be circulating at that time in the student population, and pandemic (H1N1) 2009 is probably the most likely explanation for infl uenza-like illness in recent contacts of laboratory-con- †p value for the comparison between attack rates of suspected cases among the virus-negative contacts comparing those sharing the same room and toilet with a virus-positive contact and those sharing the same room and toilet with a virus-negative contact.
‡p value for the comparison between attack rates of suspected cases among the virus-negative contacts not exposed to the virus-positive contacts compared with those quarantined in single rooms and those in double rooms. fi rmed cases. Lack of laboratory testing also means that we may have underestimated the attack rate during quarantine; some secondary infections may have been associated with asymptomatic or subclinical disease.