Sexual transmission of HIV during early infection 10 April 2003
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Peter J Flegg,
Consultant Physician
Blackpool Victoria Hospital, UK, FY3 8NR

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Re: Sexual transmission of HIV during early infection

David Rasnick requests (4 April) that I "provide the references".

I said I would willingly provide these for the statement I made. He actually quotes it word for word, but I see I need to remind him what I actually said.

"HIV is more efficiently transmitted in the acute phase of infection than subsequently. There is plenty of data verifying this, both epidemiologically and biologically, and if he wants references I will be glad to provide these".

Rasnick (again) seems to think I said something completely different, and now seems to want references for the evidence that HIV causes AIDS or that HIV is sexually transmitted. Rasnick has been given more than enough references concerning these facts in the past, not only during exchanges on fora such as the BMJ's rapid response section, but during his time on Mbekiís Presidential Panel. I will not waste everyoneís time trying to flog this particular horse, which expired a very long time ago. Also, if experience is anything to go by, he would only read into the data whatever he wishes to see. I have better things to do with my time than trot out a comprehensive list of references, only to see the material ignored, misquoted or misinterpreted.

However, concerning the evidence on HIVís efficient transmission in the acute stage of infection, here goes:

Firstly the epidemiological data. One if the first papers to look at the contribution of early transmission concluded that chains of transmission grow rapidly, and this helps explain many observed population patterns for HIV infection (1). More direct evidence accrued for this with the finding within the Swiss HIV cohort Study, which included 191 patients with PHI. Through case contact tracing and nucleic acid sequence analysis it was demonstrated that onward transmission to another partner had occurred in 17 of these cases during the time of PHI (2). A detailed analysis of 5 heterosexual couples where transmission occurred clearly demonstrated the dynamics of early HIV transmission (3).

Turning to the biological evidence, there are also data linking higher rates of transmission with high levels of virus, both in plasma and genital secretions. This has been demonstrated in the Rakai group study in Uganda (4), with the conclusion that "The viral load is the chief predictor of the risk of heterosexual transmission of HIV-1". These levels are often extremely high during PHI (5), and some individuals have seminal viral loads that consistently exceed plasma levels and are considered to be highly infectious "hyperexcretors". Pilcher has also modelled transmission and estimates that during the peak viral shedding that is associated with PHI, transmission would be 20-fold higher than that during stable chronic infection. For individuals with peak seminal viral loads of log 8.85, the probability of transmission per act would be 1.0 (i.e. transmission would occur with every single exposure), dropping to 0.03 for individuals with levels of 5.43log, down to 0.0015 for levels of 3.75log (5). Chakraborty has looked at HIVís infectiousness in 86 males and 24 females, and developed a model for calculating the probability of HIV transmission per heterosexual coital act (6). As levels of HIV-RNA rise in semen, probability of transmission increases (seminal level of log5 equating with probability of transmission of 1 per 100 episodes of intercourse).

Overall, there is plenty of evidence. This list is by no means exhaustive, but covers a spread of mutually-validating data. It would be inadvisable to ignore independently-derived evidence which lends support to a theory unless there is valid data which clearly contradict it.

(1) Jacquez JA, Koopman JS, Simon CP, Longini IM Jr. Role of the primary infection in epidemics of HIV infection in gay cohorts. J Acquir Immune Defic Syndr 1994; 7(11):1169-84. (2) Yerly S et al. HIV drug resistance and molecular epidemiology in patients with primary HIV infection. Abstract 754, 8th Conference on Retroviruses and Opportunistic Infections. Chicago 2001. (3) Pilcher CD et al. Sexual transmission during the incubation period of primary HIV infection. JAMA 2001; 286(14): 1713-4. (4) Quinn TC, Wawer MJ, Sewankambo NK, et al. Viral load and heterosexual transmission of human immunodeficiency virus type 1. N Engl J Med 342(13):921-9, 2000. (5) Pilcher CD, Shugars DC, Fiscus SA, Miller WC, Menezes P, Giner J, Dean B, Robertson K, Hart CE, Lennox JL, Eron JJ Jr, Hicks CB. HIV in body fluids during primary HIV infection: implications for pathogenesis, treatment and public health. AIDS 2001 May 4;15(7):837-45. (6) Chakraborty H, et al. Viral burden in genital secretions determines male-to-female sexual transmission of HIV-1: a probabilistic empiric model. AIDS 2001: 15(5):621-7.

Competing interests:   None declared