Infectivity of Severe Acute Respiratory Syndrome during Its Incubation Period

Objective To evaluate the infectivity of severe acute respiratory syndrome （SARS） during its incubation period by investigating chains of transmission and individuals isolated for medical observation with a view to providing scientific evidence for updating protocols of medical isolation. Methods Individuals related with the two SARS chains of transmission in Beijing in 2003 and a group of individuals isolated for medical observation in Haidian district of Beijing during the SARS outbreak were selected as subjects of study. Contactors with SARS patients and those with symptom development following the contacts were investigated via questionnaire. Serum samples were collected from super transmitters and tested for SARS-CoV antibody by neutralization test and enzyme linked immunosorbent assay （ELISA）. Results A total of 1 112 contactors were investigated in three surveys. Of them, 669 had a history of close contact with symptomatic SARS patients, 101 developed symptoms with a rate of 15.1%, 363 had a history of close contact with patients in their incubation period, none of whom developed symptoms （0%）. Serum samples were collected fi＇om 32 highly-exposed individuals, of whom 13 developing SARS symptoms atter contact had serum samples positive for SARS-CoV antibody. Samples collected from the asymptomatic contactors were all negative for SARS-CoV antibody. Conclusion SARS cases are infectious only during their symptomatic period and are non-infectious during the incubation period. Isolation for medical observation should be placed for individuals who are in close contact with symptomatic SARS patients. The results of our study are of decisive significance for the Ministry of Health to the definition of SARS close contactor.

Comparison of clinical course of patients with severe acute respiratory syndrome among the multiple generations of nosocomial transmission

Background Severe acute respiratory syndrome (SARS) is characterized by both an atypical pneumonia and efficient nosocomial transmissin. However,it remains unknown whether the infectivity and the virulence of the pathogen will change throughout the successive transmission. This study was conducted to compare the clinical features and management regimens of patients with SARS among the multiple generations from nosocomial transmission initiated by a super-spreader. Methods The clinical data of 84 epidemiologically-linked SARS patients from a hospital outbreak were retrospectively studied. All patients,in whom a clear-cut transmission generation could be noted,had a direct or indirect exposure to the index patient and the epidemic successively propagated through the multiple generations of cases within a short period of time. Results There were 66 women and 18 men with mean age of (29.2 ± 10.3) years in this cluster;and 96.4% of whom were health care workers. Detailed contact tracing identified 35 (41.7%) first-generation cases,34 (40.5%) second-generation cases,and 15 (17.8%) third-generation cases. No statistical differences among the multiple generations of transmission were found in terms of age,gender,incubation period and length of hospital stay. With the advanced transmission generations,the initial temperature lowered,the number of cases with dry cough decreased. There were no statistical differences in the peak temperature and duration of fever,other accompanying symptoms,leucopenia;however,the time from initial pulmonary infiltrates to radiographic recovery shortened ( P <0.05). No differences were found in maximum number of lung fields involved,duration from the onset of fever to the occurrence of pulmonary infiltrates and time from the initial pulmonary infiltrate to its peak among the multiple transmission generations ( P >0.05). No statistical differences were found in modes of oxygen therapy and sorts of antibiotics prescribed among the various transmission generations ( P >0.05);however, as with the advanced transmission generations,the number of cases prescribed with methylprednisolone,human γ-globulin,interferon-α,antiviral drugs (oral ribavirin or oseltamivir) increased ( P <0.05) and time from admission to starting these medication shortened ( P <0.05). Conclusions There is no evidence that SARS infection will evolve or transmit within a fashion that permits it to become less powerful throughout the successive transmission within a short time.