Since<unk> s can cause severe disease, much emphasis is placed on measures to prevent<unk> . Such a strategy usually includes restoration of the immune system as soon as possible, avoiding exposures to<unk> s agents, and using antimicrobial medications ("prophylactic medications") directed against specific<unk> s. Restoration of immune system * In patients with HIV, starting antiretroviral therapy is especially important for restoration of the immune system and reducing the incidence rate of<unk> s * In patients undergoing chemotherapy, completion of and recovery from treatment is the primary method for immune system restoration. In a select subset of high risk patients, granulocyte colony stimulating factors (G-CSF) can be used to aid immune system recovery. Avoidance of<unk> s exposure The following may be avoided as a preventative measure to reduce risk of<unk> : * Eating undercooked meat or eggs, unpasteurized dairy products or juices. * Potential sources of tuberculosis (high risk healthcare facilities, regions with high rates of tuberculosis, patients with known tuberculosis). * Any oral exposure to feces. * Contact with farm animals, especially those with diarrhea: source of Toxoplasma gondii, Cryptosporidium parvum. * Cat feces (e.g. cat litter): source of Toxoplasma gondii, Bartonella spp. * Soil/dust in areas where there is known histoplasmosis, coccidiomycosis. * Reptiles, chicks, and ducklings that are a common source of Salmonella. * Unprotected sexual intercourse with individuals with known sexually transmitted<unk> s. Prophylactic medications Individuals at higher risk are often prescribed prophylactic medication to prevent an<unk>  from occurring. A patient's risk level for developing an<unk>  is approximated using the patient's CD4 T-cell count and sometimes other markers of susceptibility. Common prophylaxis treatments include the following:<unk>  When to Give Prophylaxis Agent Pneumocystis jirovecii CD4 < 200 cells/mm3 or oropharyngeal candidasis (thrush) TMP-SMX Toxoplasma gondii CD4 < 100 cells/mm3 and positive Toxoplasma gondii IgG immunoassay TMP-SMX Mycobacterium avium complex CD4 < 50 Azithromycin
Opportunistic infection
Spillover infection
Intentional contagion of infection
Blood-borne disease
Viral pathogenesis
Superinfection
Breakthrough infection
Laboratory-acquired infection