Calculation For The Incubation Period Of SARS And Follow-up Study On The Infectiousness Of The Convalescent SARS Patients

Severe Acute Respiratory Syndrome (SARS) is a new disease caused by SARS-associated Coronavirus (SARS-CoV). High fever and exudative inflammation on chest radiography are the main clinical characters, and part patients could get respiratory distress syndrome quickly. According to the statistics from WHO, the fatality rate of SARS is 9.6%. Through a follow-up study on the convalescent SARS patients, the calculation for the incubation period of SARS and the infectiousness of the convalescent patients are analyzed in this paper.1. Calculation for the Incubation Period of SARSAccording to the incubation period, we can make a correct judgment of the time of infection, define the source of infection and formulate the periods of isolation and medical observation to the close contact person of SARS. Standardized epidemiological follow-up study questionnaire was adopted to conduct follow-up study by phone on the convalescent (1 month after discharge) patients who were reported during April and May 2003 in database of epidemiological individual cases with SARS in Beijing. Data of 32 SARS patients who had mono-source exposure were processed to build database for statistical and epidemiological analysis. Incubation period was defined through Median and Circular Distribution.According to the data, the incubation period ranged from 1d to 13d. With Median, M was 5.5d, P95 was 11.1d and QR was 4.5d. With Circular Distribution, the average angle was 163.01867, which was correspondent to 5.8d; P95 was 308.3037° , which was correspondent to 11.1d; S was 71.32306 , which was correspondent to 2.6d. When r that could measure the degree of concentration of data was 0.46080, a significant aggregation of incubation period was observed ( P<0.001 ) .According to the results with the two methods we get that the incubation period of SARS is l-13d, Mis 5.5d and mean is 5.8d. P95 is the superior limit that includes 95% SARS patients, which indicates that the longest incubation period of 95% SARS patients is 11.1d. So, it is reasonable to use 14d as the medical observation period and the isolation period of close contact person of SARS patients to make sure that the patients of incubation period can be isolated to avoid becoming sources of infection.Through the study, except analyzing angle data and day and night time data, Circular Distribution can also be used as a new method to calculate incubation period. Based on the application principle, the incubation period of SARS patients who had one time mono-source exposure was regarded as an approximate blocking circle. Every incubation period was correspondent to a place on the circle. By using Circular Distribution, we could get the concentrate position of the distribution of incubation period. The results were coincident to the tradional Median.2. Follow-up Study on the Infectiousness of the Convalescent Patients with SARSStudying the infectiousness of the convalescent patients with SARS can help people study the epidemiological law, manage source of infection and control transmission of SARS-CoV. Data of investigation were processed to build database with EXCEL2000. T-test and x2- test were used for...