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SCIENCE • VOL. 266 • 9 DECEMBER 1994 1647

REVIEWING THE DATA–II

Fulfilling Koch’s PostulatesA century ago, German bacteriologist Rob-ert Koch devised a test for proving that adisease is caused by a specific microbe. Thattest, known as “Koch’s postulates,” has be-come a standard in medicine. Peter Duesbergclaims HIV fails it. But some researchersthink recent evidence suggests the virus doespass this test.

Koch maintained that for causation to beestablished, it must be possible to isolate themicrobe from an organism that has comedown with the disease. The microbe mustthen be given to a healthy host, where itcauses the same disease; then the microbemust be isolated again. Until recently, manyAIDS researchers agreed HIV had not satis-fied Koch’s postulates, largely because thereis no good animal model for AIDS. But thoseresearchers did not agree that because HIVdidn’t satisfy Koch’s postulates, it wasn’t thecause of AIDS. They pointed out that Koch’spostulates have not been satisfied in manyother diseases where the cause has been wellestablished by other means.

But recently some leading AIDS re-searchers have stopped conceding that HIVdoesn’t satisfy Koch’s postulates, as powerfulnew evidence emerged from tragic accidents:the infection of three laboratory workerswith a pure, molecularly cloned strain ofHIV. As reported at the 1993 internationalAIDS conference in Berlin by the NationalCancer Institute’s William Blattner and hiscolleagues, one of the three lab workers de-veloped Pneumocystis pneumonia, an AIDS-defining disease, 68 months after showingevidence of infection. This lab worker hadnot received AZT (which Duesberg con-tends can cause AIDS), or any other anti-HIV drug, until 83 months after infection,when the patient had fewer than 50 CD4cells, the key immune system cells destroyedby HIV. (A healthy person typically has acount of 600 to 1200 CD4s.)

Blattner reported that a second lab worker,who also received no anti-viral drugs, had250 to 400 CD4s at 83 months. The third labworker had CD4 counts of 200 to 500 at 25months and had been given anti-virals.“These people have no other risk factors” forAIDS, such as illicit drug injection or homo-sexual sex, Blattner says.

Duesberg told Science that, in his view,the lab-worker data don’t prove that HIVsatisfies Koch’s postulates. Two of the labworkers, he notes, did not have AIDS, butonly a severe decline in CD4 counts. Dues-berg did not directly address data on the onelab worker who has the AIDS-defining ill-ness Pneumocystis pneumonia and thereforedoes have AIDS. Instead, Duesberg re-sponded by asking why, if HIV causes AIDS,

more HIV-positive people don’tdevelop this AIDS-definingpneumonia within 5 years. (Theaverage time between HIV in-fection and an AIDS-definingillness is 10 years.)

Rather than accept the lab-worker data as definitive, Dues-berg said he would like to see anepidemiologic study to answer thequestion of whether HIV causesAIDS. The study he wants would comparetwo large groups of people matched for age,lifestyle, and “non–drug use” who differ onlyin HIV status. “If the HIV-positive group hadsignificantly more AIDS-defining diseases

than the negative group, HIVcould be the cause,” Duesbergsays. But, he says, “there is noteven one study in the vastAIDS literature that showsthat an HIV-positive group of20- to 50-year-old people whodo not use drugs and do nothave congenital diseases, likehemophilia, have more AIDSdiseases than an HIV-nega-tive control group.”

Others contend that thisstudy isn’t necessary. “As faras I’m concerned, the labora-

tory workers prove causation,” says AnthonyFauci, head of the National Institute of Al-lergy and Infectious Diseases. “I don’t needany more than that.”

–Jon Cohen

Two years ago, Peter Duesberg used epide-

But then the virus began a rapid spread.

By the end of 1988, in one risk group alone—users of injectable drugs—more than 1000people had tested positive for HIV. TimBrown, a theoretical physicist at the East-West Center in Hawaii who has worked withthe Thai National Economic and Social De-velopment board to model the AIDS epi-demic, estimates that by the end of 1993more than 700,000 Thais had become in-

Postulator. Robert Koch.

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