Data from the surveys were collated for each virus according to number of 
persons at risk, number of times the virus was handled in the laboratory, type of 
laboratory facility as described in the survey instructions, and numbers of overt 
and subclinical infections with the virus. Neither survey distinguished between 
animal and tissue culture exposures. 
In the 1976 survey, respondents were requested to classify their facilities into one 
of five categories, A through E. In the second survey, the containment and 
practices were classified into four categories, Level 1 through Level 4. The 
definitions of these different categories, as included with each survey, are 
provided in Appendix D. 
Based on the information provided in the survey, SALS calculated an "experience 
factor" for each virus for each laboratory, by multiplying the number of times the 
virus was handled, (once (1), two to twenty times (2), or greater than twenty 
times (20)) by the number of people at risk (one to five (1), six to twenty (6), 
twenty-one to one hundred (21), or greater than one hundred (100)). (Numbers 
in parentheses are the multipliers used). In the following, we have adhered to the 
same conventions, with the exception that multipliers used for the number of 
people at risk are the actual numbers of workers at risk, as reported by each 
laboratory. The product of the actual number of people at risk times the number 
of times the virus was handled, is here termed "exposure experience." 
Table 10 displays the results obtained in the 1976 survey from the 48 laboratories 
reporting experience with SFV. A total of 330 workers were exposed, with an 
average exposure number per worker of 18. Over one-half (53%) of the exposure 
experience with SFV in these laboratories was at containment levels equivalent 
to the present category of Biosafety Level 1 (Level A + Level B). No overt 
infections were reported among this group; one possible inapparent infection was 
described, this individual had a hemmaglutination-inhibition (HI) assay result 
positive at a titre of 1:10, which is borderline positive. 
Among the respondents to the 1978 SALS survey (Table 11), sixteen laboratories 
employed SFV in their work, and one hundred forty additional workers were 
reported as at risk for SFV infection. Of the total exposure experience for this 
group, 15% was at Level 1 and 83% at Level 2, levels which are nearly 
equivalent, respectively, to present-day Biosafety Level 1 and Biosafety Level 
2 . 
One overt infection was reported, the fatal encephalitis discussed above. Two 
individuals in the same Tubingen laboratory were tested for antibodies to SFV: 
one was positive without an overt infection. 
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Recombinant DNA Research, Volume 18 
