Opportunistic infections are a severe complication in immunocompromised patients and in those receiving treatments that impair the homeostasis of the immunologic system. Biologics to treat autoimmune disorders are not an exception, and several reports have demonstrated an increased risk of infections produced by bacteria, fungi, and viruses.
Infection by tuberculosis bacilli increased significantly, soon after anti-TNF drugs were placed on the market. Fortunately, the implementation of measures to treat or to exclude latent tuberculosis reduced the number of cases considerably. Infections produced by fungi can be severe, but many of these infections are only frequent in some endemic geographical areas. Concerning viruses, varicella zoster has been implicated as a complication of biologic therapy. Various studies have shown its increase in patients receiving biologics, though glucocorticoids, which are frequently used as concomitant medication, appear to play a more relevant role in this complication. Finally, reactivation of chronic hepatitis B virus infection can occur if prophylactic measures with antivirals are not taken. For this reason, screening for hepatitis B virus infection before administering a biologic is necessary.