Epidemiological Study On Severe Acute Respiratory Syndrome In An Unit

Severe acute respiratory syndrome (SARS) is an emerging infectious disease that first manifested in China in November 2002 and has subsequently spread worldwide, posing great threat for the people's health. China was one of the most severely affected countries and because of its relatively high transmissibility and mortality upon infection, SARS has been included as one of the reported infectious disease in China. The military unit in Beijing has been involved in the epidemic due to its accumulative and dynamic characteristics. The epidemic investigation in military population will play important role for control of the disease. In the present study, multidisciplinary approach, including traditional epidemiological study, serum epidemiological study, as well as advanced molecular biological techniques, was combined to make systematic analysis on the SARS epidemic in military population.The first part of the study concentrates on the description and analysis of three case clusters in a military hospital. The index cases were traced to identify all the secondary cases. The SPSS and Excel software were used to analyze the temporal and geographical characteristics of the transmission. Incubation time and the possible transmission route as well as the major factors that might be associated with the widespread of the disease were disclosed.The second part focuses on antibody detection in SARS patients. Confirmed SARS patients, close contacts of the patients and the normal population group were included for IFA and ELISA evaluation. The dynamic change of the serum IgG in different period of the disease was defined. Third, the SARS viral excretion study were performed from three perspectives: ?The SARS viral RNA was detected in different kinds of clinical samples from various disease courses, the excretion profile for different sample type throughout the disease progression were explored, and the optimal specimen types and timing of specimen collection for detection were identified at the same time. ?The RT-PCR positive SARS patients were followed up for viral detection to disclose the duration of the viral excretion indifferent samples. The potential factors that might be associated with long term viral excretion were also investigated, so that the quarantine and isolation time can be obtained accordingly. For the molecular epidemiology studies of SARS-CoV, the sequence comparison was made in different patients from one cluster, different sample from one patient to disclose the adaptable mutation of the virus in the host. In addition, the possible role that the viral mutation might play in the clinical outcome was also investigated, by sequence comparison among patients with different disease outcome.The disease outbreak in military unit was mostly characterized by the initial infection source in hospital, followed by the fast dispersion into other population. The patients focused on 20 to 29 and 30 to 39 age years old. The career distribution analysis disclosed the medical care worker serve as the major population with high risk of infection. The temporal distribution of the epidemic showed dominant assembly of the cases occurrence.The result suggested that IgG antibody against SARS-CoV was not detected in hospital staff and normal population groups. The statistical analysis of the positive rate showed increasing profile in confirmed SARS patients, with low rates within 10 days, followed by rate of 64.86%, 78.13%, 93.65%, 90.48% and 100% when 20 days, 30days, 40days, 50days and 60days after disease onset, respectively. Chi-square for trend test revealed that the positive rates of IgG antibody of SARS patient increased with time progress significantly.In the RT-PCR detection for various clinical specimens, the stool specimen proved to be with higher detection rate of 21.55% (50/232). The positive rate of sputa specimen is 18.75% (27/144). The positive rates of stools and sputa were 100% and 50% respectively within 10 days after onset of the disease, and then decreased quickly. Within20 days, 30days, 40days of onset, the positive rates of S ARS-associated coronavirus was 53.33% and 54.54%, 37.81% and 33.33%, 28.25% and 20%. The epidemiological investigation did not find SARS illness in close contacts of convalescent patients during the study period* although virus can be detected in the convalescent clinical samples. In addition, the risk factor analysis showed the co-morbid conditions might be related with longer excretion duration in SARS patients.A total of 29 patients were included for mutation analysis. As a result, three 5-locus genotypes were defined: GGCTC and TGTTT genotype which were suggested to be from the middle and late epidemic in the previous study, and the GATTC genotype which wasreported for the first time. Two kinds of genotypes were identified among twelve patients from the same case cluster. The sequence results, in combined with epidemiological information suggest the five SNPs might represent as phase specific, instead of lineage specific signature. In addition, the comparisons among different samples from the same patient indicated no nucleotide variation in any position of the five amplified fragments. Also, sequence alignment did not disclose the characteristic signature for the severe disease. The findings might help to understand the viral genetic diversity and the adaptable mutation of the virus in the host.In summery, the comprehensive findings in this study can help us to get a full understanding of the whole epidemiology of SARS-related viruses. This will hopefully serve as evidence of guidelines for the prevention and control of the disease outbreak among humans.