Pneumocystis jirovecii pneumonia

Acute HIV infection, also called the acute retroviral syndrome, is the symptomatic viremic phase in the days to weeks after HIV acquisition, presenting with fever, fatigue, myalgia, rash, and pharyngitis at a time when antibody testing may still be negative. Diagnosis requires an HIV RNA viral load, and antiretroviral therapy should begin as soon as the patient is ready, regardless of CD4 count.

ARDS is acute (within 1 week), bilateral, non-cardiogenic hypoxemic respiratory failure from diffuse alveolar damage, diagnosed by the 2012 Berlin criteria and graded by the Pao2/Fio2 ratio. Management is lung-protective ventilation, PEEP titration, early prone positioning for severe disease, conservative fluid strategy, and treatment of the inciting insult.

Community-acquired pneumonia is a lower respiratory tract infection acquired outside the hospital that is diagnosed by a compatible clinical syndrome plus a new infiltrate on chest imaging, risk-stratified with CURB-65 or the Pneumonia Severity Index to guide site of care, and treated with empiric antibiotics chosen by site of care and comorbidity, escalating to cover MRSA or Pseudomonas aeruginosa when risk factors are present.

Cytomegalovirus is a ubiquitous herpesvirus that is usually asymptomatic or causes a heterophile-negative mononucleosis-like illness in healthy hosts, but reactivates to cause retinitis, colitis, pneumonitis, or encephalitis in transplant recipients and patients with AIDS; treatment is systemic ganciclovir or valganciclovir, with foscarnet and cidofovir reserved for resistance or intolerance.

Histoplasma capsulatum is an endemic dimorphic fungus, acquired by inhalation of conidia in the Mississippi and Ohio River valleys and other endemic regions, that most often causes asymptomatic or mild pulmonary infection but can disseminate in immunosuppressed hosts; diagnosis rests on the Histoplasma urinary antigen assay and treatment is itraconazole for mild to moderate disease or liposomal amphotericin B followed by itraconazole for severe or disseminated infection.

Coccidioidomycosis, or valley fever, is a dimorphic fungal infection acquired by inhaling Coccidioides arthroconidia in the southwestern United States, ranging from self-limited pneumonia to disseminated or meningeal disease, diagnosed by culture, histopathology, or serology and treated with fluconazole for symptomatic disease and lifelong fluconazole for meningitis.

Toxoplasmosis is infection with the protozoan Toxoplasma gondii, acquired from undercooked meat or cat feces, causing a mononucleosis-like illness in immunocompetent hosts, reactivation encephalitis with ring-enhancing brain lesions in advanced HIV, and a severe congenital syndrome after maternal primary infection in pregnancy. Diagnosis in CNS disease is largely presumptive on serology, imaging, and empiric treatment response, and management is pyrimethamine-sulfadiazine-leucovorin, with prevention centered on CD4-based prophylaxis and food/cat-litter precautions in pregnancy.

Tuberculosis, caused by Mycobacterium tuberculosis, remains a leading global cause of infectious death and presents as latent infection, primary/secondary pulmonary disease, or extrapulmonary and disseminated (miliary) disease. Diagnosis rests on AFB smear, NAAT, and mycobacterial culture (the gold standard), and drug-susceptible active disease is treated with a four-drug regimen (isoniazid, rifampin, pyrazinamide, ethambutol) for 2 months followed by isoniazid plus rifampin for 4 to 7 months.

Pneumothorax is air in the pleural space, occurring spontaneously (primary in structurally normal lungs, secondary in underlying lung disease) or from trauma or procedures. Management is driven by size and hemodynamic stability, ranging from observation to needle aspiration to tube thoracostomy.

Interstitial lung disease (ILD), also called diffuse parenchymal lung disease, is a diverse group of nonmalignant disorders causing inflammation and scarring of the alveolar interstitium, presenting as subacute to chronic exertional dyspnea and nonproductive cough. Diagnosis rests on pulmonary function testing plus high-resolution CT pattern recognition; management is exposure removal, glucocorticoids for inflammatory disease, antifibrotic therapy for progressive fibrotic disease, oxygen for hypoxemia, and early transplant referral.