CDC Fact Sheet - December 3, 1993
Centers for Disease Control and Prevention

An important goal of epidemiologic and laboratory research on the human immunodeficiency virus (HIV) has been to determine how HIV transmission occurs, so that effective prevention strategies can be developed. Early in the epidemic, epidemiologic studies of persons with the acquired immunodeficiency syndrome (AIDS) defined the most common modes of transmission--sexual, blood-borne, and perinatal--making strategies for prevention possible even before HIV was discovered. With the advent of serologic testing for HIV, the risk of transmission was estimated for certain exposures that transmit HIV less frequently, such as needle-stick injuries, providing the rationale for guidelines to prevent transmission in such situations. More recently, genetic sequencing has been used as a molecular epidemiologic tool to pinpoint the source of HIV transmission in settings where it is even less common, thereby allowing prevention strategies to be extended even further1. In this issue of the JOURNAL, Fitzgibbon and collaborators report their use of genetic sequencing to document HIV transmission from one child to another, raising questions about the magnitude of the risk of HIV transmission between children and other household members and the measures appropriate to prevent it2.

The laboratory and epidemiologic findings of this investigation indicate that HIV was transmitted from child 1 to child 2. The absence of HIV infection in child 2 at one year of age and the dissimilarity of the HIV genomes from child 2 and child 2's mother exclude the possibility of mother-to-child transmission. The high degree of concordance in the V3 nucleotide sequences of viruses from the two children is comparable to that reported for other epidemiologically linked infections,1,3,4 and the presence in both children of a mutation associated with zidovudine resistance provides further evidence of the relatedness of the infections. Although the mode of transmission was not definitively identified, it most likely involved an undocumented exposure of the skin or mucous membranes of child 2 to the infected blood of child 1. Opportunities for such exposures between the two children were identified, and child 2 had open skin lesions that may have facilitated transmission.

How common is such transmission? HIV infection has resulted from contact between skin or mucous membranes and infected blood during the provision of health care in both institutional settings and the home. However, among health care workers monitored prospectively after more than 1100 mucous-membrane exposures to HIV-infected blood, there was only one seroconversion, yielding an estimated transmission rate of 0.09 percent (95 percent confidence interval, 0.006 to 0.5 percent) The risk of transmission after cutaneous exposure to HIV-infected blood is probably smaller, since no instances of transmission were observed after more than 2700 reported exposures (95 percent confidence interval for transmission rate, 0 to 0.11 percent)

Blood contact may go unrecognized, however, when the amount of blood is small and the exposed person inattentive to the exposure. Opportunities for such contact may arise among household members, especially children. Nevertheless, available data suggest that in settings where such exposures may occur, HIV is very rarely transmitted. There are only two reports of apparent HIV transmission from infected children to siblings in the absence of recognized exposures to blood. One brief report suggested biting as the route of transmission, although the authors did not mention contact with blood and had no molecular data to confirm transmission.10 The other investigation suggested that transmission occurred through undocumented percutaneous exposure to blood1. In contrast, 17 studies of persons in the United States and Europe who had contact in the household, not involving sex or shared needles, with HIV-infected persons found no infections among more than 1100 people, including more than 300 children, who were followed for more than 1700 person-years (95 percent confidence interval for the rate of transmission, 0 to 0.2 infections per 100 person-years).

As Fitzgibbon and colleagues demonstrate, on rare occasions HIV can be transmitted between household members in the absence of sexual, percutaneous, or documented blood contact. Therefore, even though the risk of such transmission is extremely small, precautions are warranted to prevent contact with blood in households and similar settings.

Recommendations have been published for preventing exposure to blood in health care settings, other workplaces, athletic fields, schools, and day-care centers.11-13 Similar precautions should be taken in households and other settings when there are persons who are infected with HIV or other blood-borne pathogens, or of unknown infection status. Appropriate barrier precautions should be used to prevent skin and mucous membranes from coming into contact with blood. Hands and other parts of the body should be washed immediately after contact with blood. When blood or blood- containing fluids are spilled, they should be removed promptly and the contaminated surfaces cleaned with bleach at a dilution of 1:10 to 1:100. Practices that increase the likelihood of blood contact, such as the sharing of razors and toothbrushes, should be avoided. Needles and other sharp instruments should be used only when medically necessary and should be handled according to the recommendations made for health care settings. All persons providing health care should be trained in proper techniques of infection control. Finally, patients with blood-borne infections should be informed that their blood may be infectious and should be advised of the importance of keeping it from contacting others. Adherence to these guidelines should further reduce the risk of HIV transmission, even in situations where the risk is already extremely low.

In homes, schools, and day-care centers, children may live, learn, and play with children who have HIV infection or whose HIV-infection status is unknown. Because the risk of transmission in these settings is extremely low, HIV-infected children should not be excluded solely on the basis of their infection. Persons caring for children should be trained in, and adhere to, proper infection-control techniques.13 To reduce the risk of transmission further, appropriate precautions against exposure to blood should be followed, with special attention paid to protecting young children, who may be unable to prevent such exposures on their own. Extra attention may be needed to ensure that open lesions are completely covered and that toothbrushes or other items that may be contaminated by blood are not shared. Young children should be kept away from sites where medical procedures are being performed on others and exposure to blood is possible.

As the HIV epidemic continues into its second decade, cases of transmission in unusual settings may be recognized, with their detection facilitated by new laboratory techniques. Although it is important to investigate these rare cases promptly and thoroughly, it is equally important to view them in the proper perspective. The vast majority of HIV-infected persons do not transmit the virus except by the well-recognized routes. Although instances such as the one described by Fitzgibbon and colleagues may bring calls for more extreme measures to prevent HIV transmission in all settings, physicians, policy makers, and the public must recognize that such measures may lead to unwarranted and unnecessary discrimination against HIV-infected persons and can never reduce the risk to zero. Prevention of HIV transmission through unprotected sex, through needle sharing, and from mother to child must remain our nation's primary focus in responding to the HIV epidemic.

R.J. Simonds, M.D. Martha F. Rogers, M.D.

Centers for Disease Control and Prevention Atlanta, GA 30333

REFERENCES

1. HIV infection in two brothers receiving intravenous therapy for hemophilia. MMWR 1992;41:228-31.

2. Fitzgibbon JE, Gaur S, Frenkel LD, Laraque F, Edlin BR, Dubin DT. Transmission from one child to another of human immunodeficiency virus type 1 with a zidovudine-resistance mutation. N Engl J Med 1993;329:xxx-xx.

3. Ou C-Y, Ciesielski CA, Myers G, et al. Molecular epidemiology of HIV transmission in a dental practice. Science 1992;256:1165-71.

4. Burger H, Weiser B, Flaherty K, Gulla J, Nguyen PN, Gibbs RA. Evolution of human immunodeficiency virus type 1 nucleotide sequence diversity among close contacts. Proc Natl Acad Sci U S A 1991;88:11236-40.

5. Ippolito G, Puro V, De Carli G, Italian Study Group on Occupational Risk of HIV Infection. The risk of occupational human immunodeficiency virus infection in health care workers: Italian Multicenter Study. Arch Intern Med 1993;153:1451-8.

6. Henderson DK, Fahey BJ, Willy M, et al. Risk for occupational transmission of human immunodeficiency virus type 1 (HIV-1) associated with clinical exposures: a prospective evaluation. Ann Intern Med 1990;113:740-6.

7. Grint P, McEvoy M. Two associated cases of the acquired immunodeficiency syndrome (AIDS). Communicable Disease Report 1985;42:4.

8. Apparent transmission of human T-lymphotropic virus type III/lymphadenopathy-associated virus from a child to a mother providing health care. MMWR 1986;35:76-9.

9. Update: Human immunodeficiency virus infections in health-care workers exposed to blood of infected patients. MMWR 1987;36:285-9.

10. Wahn V, Kramer HH, Voit T, Bruster HT, Scrampical B, Scheid A. Horizontal transmission of HIV infection between two siblings. Lancet 1986;1:694.

11. Simonds RJ, Chanock S. Medical issues related to caring for human immunodeficiency syndrome-infected children in and out of the home. Pediatr Infect Dis J 1993;12:845-52.

12. Recommendations for prevention of HIV transmission in health-care settings. MMWR 1987;36:(suppl 2S):1S-18S.

13. Staffing. In: American Public Health Association, American Academy of Pediatrics. Caring for our children--national health and safety performance standards: guidelines for out-of-home child care programs. Washington, DC: American Public Health Association, 1992;24-8.