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July 30, 1997
Some of the consultants who advise the Centers for
Disease Control and Prevention (CDC) on AIDS, and even an agency employee, say
last week's discussions to establish guidelines for HIV postexposure therapy
(PET) are based on a premise about efficacy that may not be valid.
At the root of that premise is a case-control study published two years ago in the agency's Morbidity and Mortality Weekly Report (MMWR), which reported that healthcare workers accidentally exposed to HIV-infected blood through percutaneous injury had 79% less chance of developing infection if they were treated with zidovudine after the exposure. "I was really concerned because I saw a lot of people making recommendations based on the case-control study and I saw a lot of data using 79%," said Dr. Denise Cardo of the CDC. "We don't know if it's applicable. The study has a lot of limitations."
Some of those limitations include a small sample size and biases introduced because the data were collected from three different countries--the US, the UK and France--and at different times. Additionally, US data on accidental exposures was obtained through a "passive surveillance project" involving 300 hospitals; of those, 190 supplied data to the CDC for the study.
One of the agency's external consultants voiced his opinion unequivocally. "There is not a 79% reduction," said Alfred Saah of the Merck Research Lab in Blue Bell, Penn. "That's an enormous reduction. Are we going to build this building on a foundation of 79%?" Saah says if the CDC issues guidelines on PET based on the case-control data, it may set a standard of care that doesn't exist. "I'm afraid we're going to create an expectation we're not going to be able to deliver on. We are really flying by the seat of our pants."
"I don't believe the 79% stuff, either," said Dr. Alastair W. McLeod of Vancouver, BC. "I think it probably works, but it's not that good." McLeod said the PET issue is a potential "quagmire" for the CDC, since accurate data on the efficacy of postexposure therapy could be many years away.
Efficacy aside, some HIV workers worry that if postexposure prophylaxis becomes the norm it will undermine prevention efforts. "One of the major fears we have is that guidelines on PET will only further erode the advances we've made over the past decade in behavioral change," said Randy Pope, chief of the HIV/AIDS Prevention and Intervention section of the Michigan Department of Community Health. Pope says risky behavior is on the rise anyway among HIV patients, due in part to new, more efficacious drug therapies. PET would only make it worse.
Hospital emergency departments may bear the brunt of patients seeking postexposure therapy, said Dr. Richard Rothman of Johns Hopkins Hospital in Baltimore, Maryland, and that raises the issue of cost. He pointed out that, even though patients may perceive postexposure treatment as an emergency, insurance companies--if the patient has insurance--might not agree, and that directly affects whether the hospital will get paid for providing prophylaxis.
The CDC says it may have draft guidelines for PET available by year's end, and final recommendations sometime next year.
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