One of these individuals (PV) seroconverted between 1978 and 1981. These 
results are presumptive evidence of low-grade SFV infection; however, because 
this laboratory also handled other alphaviruses, it is difficult to exclude the 
possibility that some of the apparent positives result from infection by viruses 
antigenically similar to SFV. 
In summary, serological data from two sites, comprising thirty-two laboratory 
workers exposed to SFV over a period of five years or more, suggest that low- 
level, inapparent SFV infection occasionally can occur. The experience of these 
two laboratories contrasts in several regards: Each used a different strain of SFV; 
one worked exclusively with animals, the other only with tissue culture; and they 
recorded markedly different frequencies of SFV seroconversion. In one matter, 
however, their experience coincided: neither recorded an overt SFV infection 
among any of their laboratory workers. 
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Recombinant DNA Research, Volume 18 
