Transmission of HIV in the health care delivery setting has been the subject of intense investigation throughout the course of the epidemic. The percentage of health care workers with AIDS who have “no identified risk” for HIV infection has remained low (< 10%) and has not increased over time, despite the dramatic increase in the number of AIDS cases and concomitant exposure of health care workers to patients with HIV disease. More importantly, detailed studies examining the risk of specific exposures, such as needle stick injuries and mucous membrane exposures, have demonstrated very low risk of disease acquisition in the workplace. More than 3628 health care workers have been examined prospectively in carefully designed surveillance studies at 10 high-incidence medical centers.

The overall risk of seroconversion after a percutaneous needle stick from a known HIV-positive source is 0.25% per exposure. Although mucous membrane exposures to HIV-positive blood have resulted in seroconversion in at least three health care workers, prospective studies of over 900 splash exposures have failed to identify any seroconverters, implying that the risk of infection is even lower after mucous membrane exposure than through percutaneous needle stick.

To date, no transmission has occurred after exposure to body fluids other than blood or fluids heavily contaminated with blood. Therefore, although the potential for HIV transmission to health care providers clearly exists, the risk of infection is inherently low and can be further minimized by following routine precautions to prevent transmission.

Prevention
In August 1987, the Centers for Disease Control and Prevention (CDC) published guidelines designed to minimize health care worker exposure to blood and body fluids which may be infected with blood-borne pathogens, such as HIV. These guidelines remain the principal mode of HIV prevention among health care workers today. These so-called universal precautions are based on the premise that any patient may be infected with blood-borne infectious agents and it may be difficult, if not impossible, to differentiate those with infection from their uninfected counterparts. Thus all specimens containing blood or blood-tinged fluids obtained from any patient should be considered hazardous and handled as such (Table 410-2) .

Handwashing is the cornerstone of universal precautions, as it is with all infection-control practices. Gloves should be worn when spillage of blood or body fluids is likely. Gloves should never be washed and should be changed after soiling or after gross contamination, with handwashing immediately after the gloves are removed. Gowns, protective eyewear, and masks usually are not needed except in circumstances in which splattering or splashing of blood-containing fluids is likely to occur. Masks should always be worn in situations in which eyewear is required. Reusable equipment should be cleansed of visible organic material, placed in an impervious bag, and returned to central supply for decontamination. Although heat is the single best decontamination method, chemical agents that possess mycobactericidal activity are effective against both hepatitis B and HIV and are acceptable alternatives when heat inactivation is impractical. Blood spills should be cleaned with appropriate caution.

After placing gloves and other appropriate barrier precautions, excess blood should be removed with absorbent materials (e.g., paper towels), the area then cleaned with soap and water, and the area disinfected with a 1:10 solution of sodium hypochlorite (household bleach) and water. Health care workers with denuded skin, open lesions, or active dermatitis should avoid direct patient contact and should not process contaminated equipment or materials. Private rooms generally are not required for patients known to be HIV infected unless a concomitant opportunistic disease is present which requires respiratory, enteric, or contact isolation. Food service should be provided as usual on reusable dishware.

Because all blood and body fluids should be handled as potentially hazardous and all patients presumed to be infected, it makes little sense to identify infected patients or their specimens with “blood and body fluid” labels. The use of such labels on known infected patients implies that unlabeled specimens or specimens from patients of unknown status are less hazardous and may be handled with less care. Indeed, studies have shown that more than half of the specimens containing antibodies to either HbsAg or HIV went to the laboratory unlabeled. The handling of sharp instruments (“sharps”) represents the greatest risk of HIV transmission to health care workers. Although sharp injuries cannot be entirely eliminated, the number of exposures can be reduced substantially by adhering to guidelines put forth in universal precautions. Before a sharp instrument is used, thought should be given regarding where the instrument will be disposed after use. Impervious containers should be readily available in all patient care areas and identified by the health care worker prior to “sharp” utilization. The containers should be checked frequently and should not be allowed to overfill. Used needles should never be manipulated, bent, broken, or recapped. Recapping of needles is the single most common activity that results in needle stick injuries.

Despite their logical basis and relative ease of implementation, universal precautions have not been used routinely by many health care providers. Recent studies have shown that > 50% of health care workers engage in inadequate infection control practices, even in high-impact AIDS centers, and up to 40% of the needle stick exposures were judged to be preventable. Although lack of adequate education may partly explain these findings, implementation of infection control practices has been generally poor historically. Between 200 and 400 health care workers die each year as a result of hepatitis B infection acquired on the job. The use of universal precautions helps minimize the transmission of many transmissible diseases in addition to HIV.

Even in the best of circumstances, accidental mucous membrane and percutaneous exposures to blood from HIV-infected patients do occur. Each institution and health care facility should adopt procedures for managing these exposures based on guidelines published by the CDC (recently updated; MMWR 47(RR-7): 1-28, 1998). The essential elements of management following needle stick or mucous membrane exposure include defining the type of exposure, appropriately evaluating the donor (patient) and recipient (health care worker) at the time of exposure, and follow-up of the health care worker for at least 1 year after exposure.

Proposed definitions of the types of exposure are summarized in Table 410-3 . Health care workers with any kind of parenteral exposure should be counseled and evaluated for possible acquisition of HIV and receive routine prophylaxis against hepatitis B. The source patient (donor) should be evaluated for HIV infection; if the donor’s HIV status is unknown, the donor should be informed about the incident and encouraged to allow voluntary, confidential screening of his/her blood for HIV and hepatitis B antibody.

If the patient refuses or cannot give consent, he/she should be considered to be infected. In cases where exposure to HIV is documented or presumed to have occurred, the health care worker should be evaluated serologically for the presence of HIV as soon as possible after the exposure (baseline) and again at 6 weeks, 12 weeks, 24 weeks, and 1 year after the exposure to determine whether HIV transmission has occurred. The health care worker should report any acute illnesses that occur during the follow-up period, especially during the first 6 to 12 weeks after exposure.

Exposed workers should follow the recommended guidelines for preventing HIV transmission, including using safe sexual practices; refraining from blood, semen, and organ donation; and avoiding breast feeding. If the source patient is seronegative for HIV and has no clinical manifestations of HIV disease, no further follow-up of the exposed health care workers is necessary, although some workers prefer follow-up for their own peace of mind. Serologic testing should be made available to all health care workers who are concerned about potential on the job exposure.

The use of chemoprophylaxis following parenteral exposure to HIV is now routinely recommended for all health care workers who experience a massive or definite parenteral exposure. Many clinicians favor using prophylactic antiretroviral therapy after possible parenteral exposures, although this practice remains controversial. The firm recommendation to administer routine chemoprophylaxis in cases of massive or definite exposure is based on increasing evidence of the beneficial protective effects from its use in both animal and human studies. In some animal models of retroviral infection, zidovudine (ZDV), when given early after inoculation, modifies the course of disease.

Very recent reports from the CDC indicate an 80% reduction in anticipated transmission rates of HIV to parenterally exposed health care workers who had received ZDV prophylaxis. With the introduction of more potent antiretroviral therapy, even more reduction in HIV transmission in the health care worker setting is anticipated. Therefore, in most medical centers, multidrug chemoprophylaxis has become a standard of practice. The CDC recommends use of at least a dual nucleoside regimen (e.g., zidovudine with lamivudine), with or without the addition of a third agent, usually a potent protease inhibitor or a non-nucleoside reverse transcriptase inhibitor.

Health care workers with doubtful parenteral or nonparenteral exposures generally should not take chemoprophylaxis. The optimal timing and dosage of chemoprophylaxis are unknown; however, animal studies suggest that higher doses given as soon as possible after exposure have the best chance of being effective. Therefore, most centers that offer chemoprophylaxis to their employees have established mechanisms whereby the health care worker can be evaluated and the drugs administered within 2 to 4 hours after the exposure. Standard doses of the antiretroviral agents are administered for 4 to 6 weeks.