Human Immunodeficiency Virus: Fragments of the Puzzle

IN THIS ISSUE OF THE JOURNAL. TWO IMPORTANT PAPERS (pages 290. 295) describing the progress of the human immunodeficiency virus (HIV) epidemic in Canada are published. Changes in the demographics of this disease in the United States are welldescribed and document a steady shift to less advantaged groups in society including intravenous drug abusers. individuals in the sex trade and certain members of the immigrant population . The fragmentary data available to us from epidemiological studies in Canada suggest that the shift in Canada is not as marked as that observed in the United States. but the e.>..'"])ectation is that similar trends will be observed. Our knowledge of the extent of infection and impact of this virus in Canada, however. is described poorly. What do we know about the current status of this most important public health problem at the end of the 20th century? The paper by Ricketts et al. from the Laboratory Centre for Disease Control. is reassuring. A surveillance system enrolling s ubj ects from across Canada to follow s ignificant occupational exposure to HN has failed to document prospectively any case of transmission of the virus occupationally in Canada afte r six and one-half years. One recent anecdotal report (1) does suggest possible occupational acquisition by a technologist early in the epidemic. before current programs to prevent transmission were in place and before this surveillance program was initiated. Studies from the United Stales (2) have documented U1al tile risk of acquiring HN infection following needlestick exposure to a known inJected patient is 0.3 to 0 .5%. The risk likely is greater when th e exposu re allows inocu lation of greater quantities of blood. This low rate of transmission . compared with agents such as hepatitis B. reflects the low inoculum of infectious virus present in the blood of most individuals infected witil HIV. Given these reported tra nsmission rates it is not surpris ing witi1 the numbers of episodes enrolled in tile Canadian Surveillance Study tilat an episode of prospectively docu mented occupational transmission in Canada has not been observed. The study confirms. however. U1al in