Aspiration or influenza in the nursing home—consider Staphylococcus aureus.

Trip to southwestern United States—consider Coccidioidomycosis.

Trip to Southeast Asia—consider melioidosis or tuberculosis.

HIV patient from New York City with cough, fever, and night sweats—consider multidrug-resistant tuberculosis.

Resident of the desert southwestern United States with exposure to rodent excreta—consider Hantavirus pulmonary syndrome.

Return from Pacific Northwest, not responding to therapy— consider Cryptococcus gattii.

Acute presentation and localized findings—consider typical pathogens such as Streptococcus pneumoniae, Haemophilus influenzae, and the enteric gram-negative organisms.

Subacute presentation and absent or diffuse findings— consider atypical pathogens such as Mycoplasma, Chlamydophila, and viruses.

Rapid progression—consider S. pneumoniae (severe), Staphylococcus aureus, or Legionella.

Poor dentition and foul-smelling sputum—consider a polymicrobial lung abscess.

Bullous myringitis—consider Mycoplasma pneumoniae.

Absent gag reflex or altered sensorium—consider aspiration.

Encephalitis—consider M. pneumoniae or Legionella pneumophila.

Cutaneous manifestations include erythema multiforme (M. pneumoniae), erythema nodosum (Chlamydophila pneumoniae and Mycobacterium tuberculosis), or ecthyma gangrenosum (Pseudomonas aeruginosa).

Exposure to construction sites or old buildings with accumulations of bat or bird droppings—consider Histoplasma capsulatum or Cryptococcus neoformans.

Hunters who skin their own rabbits—consider Francisella tularensis.

Farmers working with stored hay, marijuana smokers— consider Aspergillus species.

HIV patients—consider common pathogens, Pneumocystis jirovecii, cytomegalovirus, Mycobacterium aviumintracellulare, H. capsulatum, Coccidioides immitis, and C. neoformans.

Neutropenic patients—consider Aspergillus species.

Immunosuppressive medications—consider various viral, fungal, and mycobacterial agents.

Alcoholism—consider aspiration pneumonia with mixed flora, as well as tuberculosis.

Chronic obstructive pulmonary disease (COPD)—consider Moraxella catarrhalis, H. influenzae, and S. pneumoniae.

Diabetes mellitus—consider S. aureus.

Functional or surgical asplenia—consider S. pneumoniae and H. influenzae.

Treatment with tumor necrosis factor inhibitors—consider tuberculosis reactivation and endemic mycoses such as histoplasmosis.