Scientists have detected two cases in which the AIDS virus has been transmitted from one child and one adolescent to others but apparently not by the usual routes. The most likely cause is believed to be that infected blood from one entered the other through a cut or disease that broke the skin.
Such a mode of transmission has rarely, if ever, been documented before.
New York state Health Commissioner Mark R. Chassin said yesterday, "I am very concerned that there may be an over-reaction to these isolated cases."
He added: "There is absolutely no reason to panic, to believe there is any dramatically increased risk to anybody contracting the disease."
In both cases, the child and adolescent are believed to have acquired the human immunodeficiency virus, which causes AIDS, from another child or teen-ager living in the same household.
"The most likely possibility is that the virus was transmitted through exposure to blood, but since it was not observed, it could not be documented, and thus the mode of transmission could not be proved," a health care worker familiar with both cases said in an interview.
"What is disconcerting about it is, whatever the exposure was, it was not recognized. We just can't put our finger on it."
A spokesman for the New York City Health Department, Steven Matthews, said senior AIDS experts in the department had been aware of the two reported cases for several weeks and had met Friday to determine whether any change was required in public policy, which lets infected children attend schools and day care centers.
"No change is needed whatsoever," Mr. Matthews said. "Our concern about these two cases is that they will cause unnecessary fear and panic and potentially generate calls for exclusion of children or mandatory disclosure or testing that will lead to discriminatory actions."
One case involves a pair of young boys in New Jersey. The other involves two teen-age brothers, each with hemophilia. The locales have not been identified, to protect the boys' privacy.
Doctors know that one child infected the other because the strains of HIV are virtually identical.
The experts who investigated the cases found no evidence for the usual modes of transmission, that is, sexual intercourse and contaminated needles from drug abuse. Thus they believe the most probable route of transmission in both cases was blood mingling during a nosebleed or through a shared razor blade.
But experts view it as no cause for grave concern, seeing it more as one of the rare types of transmission bound to come to light as the number of thoroughly investigated cases increases.
The transmissions occurred as long as two years ago, and the cases have been under investigation for more than six months.
A report on one set of cases, the boys in New Jersey, is due to be published in the Dec. 16 New England Journal of Medicine, but people who are informed about the report are bound by rules of the journal not to discuss it before publication.
A separate report on the two hemophiliac brothers is due to be published Dec. 17 by the Centers for Disease Control and Prevention in Atlanta.