Current evidence indicates that the length of survival for patients with the
acquired immunodeficiency syndrome (
AIDS) is increasing, thereby affording a greater opportunity for strategies designed to prevent the
infectious diseases that mark the syndrome. Because these
infections may occur at different stages of immunosuppression caused by the human immunodeficiency virus (HIV), effective application of preventive measures depends not only on detection of
HIV infection but also on the use of staging indicators. The diseases that serve to define
AIDS, such as
Pneumocystis carinii pneumonia, tend to occur late in the course of
HIV infection and often when the T helper lymphocyte (CD4+ cells) count is less than 0.2 x 10(9)/l. Other
infections, such as
tuberculosis and pyogenic
bacterial pneumonia, may develop at any point after
HIV infection has occurred. Given this relation between the degree of immunosuppression and the occurrence of particular pulmonary
infections, different preventive interventions should be applied at different times. It is now known that the incidence of several of the pulmonary
infections that are common in patients with
HIV infection can be reduced by prophylactic measures.
Pneumocystis pneumonia is decreased in frequency by any one of several prophylactic agents, the best established being
pentamidine administered as an inhaled
aerosol. The role of
isoniazid in the
chemoprophylaxis of
tuberculosis in patients not infected with HIV is well established. Although there is little evidence of benefit so far from
isoniazid in HIV infected patients with a positive
tuberculin skin test response, it is logical to assume that there could be some effect. The use of
pneumococcal polysaccharide vaccine may also be of some benefit in reducing the frequency of
pneumococcal pneumonia in patients with
AIDS. In addition to these specific measures, the
antiretroviral agent zidovudine decreases both the frequency and the severity of opportunist
infections, at least during the first few months of treatment. A comprehensive strategy for prevention of HIV associated lung
infection first requires detection of
HIV seropositivity, staging the immunosuppression by the CD4+ cell count, and determining whether tuberculous
infection is present by a
tuberculin skin test. All seropositive individuals should be given
pneumococcal vaccine and those with evidence of
tuberculosis infection should be treated with
isoniazid for one year.
Zidovudine should probably be started when CD4+ cell counts are in the range 0.4-0.5 x 10(9)/l and prophylaxis against
pneumocystis infection when CD4+ cell counts are in the range 0.2-0.3 x 10(9)/l.