BACKGROUNDSevere acute respiratory syndrome (SARS) is characterized by both an atypical pneumonia and efficient nosocomial transmission. 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.

METHODSThe 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.

RESULTSThere 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 gamma-globulin, interferon-alpha, antiviral drugs (oral ribavirin or oseltamivir) increased (P < 0.05) and time from admission to starting these medication shortened (P < 0.05).

CONCLUSIONSThere 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.