Mycoplasma pneumoniae infection

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.

Legionella pneumophila is an intracellular, water-borne gram-negative bacillus causing severe community-acquired pneumonia with prominent gastrointestinal and hepatic features, confirmed by urinary antigen testing and treated with a macrolide or fluoroquinolone rather than a beta-lactam.

Infectious mononucleosis is a systemic illness caused mainly by Epstein-Barr virus, presenting with fever, pharyngitis, and lymphadenopathy, confirmed by heterophile antibody or EBV-specific serology, and managed supportively with contact-sport restriction to prevent splenic rupture.

Influenza is an acute orthomyxoviral respiratory illness with abrupt fever, myalgia, and cough, driven by an H and N surface glycoprotein antigenicity that drifts yearly (seasonal epidemics) and occasionally shifts (pandemics). Diagnosis is clinical or confirmed by nucleic acid amplification testing, and neuraminidase-inhibitor or endonuclease-inhibitor antiviral therapy started within 48 hours of onset shortens illness and reduces complications in high-risk patients.

Pneumocystis jirovecii pneumonia is a subacute, often hypoxic pneumonia in patients with CD4 counts below 200/mcL or comparable immunosuppression, diagnosed by organism visualization on induced sputum or bronchoalveolar lavage and treated with 21 days of high-dose trimethoprim-sulfamethoxazole plus adjunctive steroids when hypoxic.

Q fever, caused by inhalation of Coxiella burnetii aerosols from infected livestock, most often produces a self-limited febrile illness with atypical pneumonia or hepatitis, but it is a major cause of culture-negative endocarditis when infection becomes chronic. Acute disease is treated with doxycycline for 2 weeks; endocarditis requires combination therapy for more than 18 months.

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.

Whooping cough is a highly infectious bronchitis caused by the gram-negative coccobacillus Bordetella pertussis, marked by catarrhal, paroxysmal, and convalescent stages with lymphocytosis; diagnosis is clinical, confirmed by nasopharyngeal PCR, and treated with azithromycin plus prophylaxis of close contacts.

Erythema multiforme is an acute, immune-mediated eruption of distinctive target lesions on the distal extremities, palms, and soles, most often triggered by herpes simplex virus and, less often, Mycoplasma pneumoniae or drugs. Diagnosis is clinical, based on the classic three-zone target lesion and a negative Nikolsky sign, and treatment is symptomatic, with antiviral suppression reserved for frequent herpes-associated recurrences.

Stevens-Johnson syndrome is a severe, usually drug-induced mucocutaneous reaction with full-thickness epidermal necrosis and detachment of less than 10% body surface area. The culprit drug must be stopped immediately and the patient managed in a burn or intensive care unit with SCORTEN-guided supportive care.

Guillain-Barre syndrome is an acute, post-infectious autoimmune polyradiculoneuropathy causing rapidly progressive ascending flaccid weakness and areflexia. Diagnosis is clinical, supported by albuminocytologic dissociation on CSF and demyelinating changes on electrodiagnostic studies; first-line treatment is IVIG or plasma exchange with close monitoring for respiratory failure.

Autoimmune hemolytic anemia is antibody-mediated red cell destruction confirmed by a positive direct antiglobulin (Coombs) test, split into warm IgG disease with splenic clearance and spherocytes and cold agglutinin IgM disease with complement-mediated agglutination worse in the cold. Warm disease is treated with glucocorticoids first and cold agglutinin disease with cold avoidance and rituximab, and roughly half have an identifiable secondary cause that must be sought and treated.

Mycoplasma genitalium is an emerging sexually transmitted pathogen and a leading cause of nongonococcal, nonchlamydial urethritis in men and of cervicitis and pelvic inflammatory disease in women. Diagnosis requires nucleic acid amplification testing, and treatment is resistance-guided, with doxycycline lead-in therapy followed by extended azithromycin or moxifloxacin because macrolide resistance is increasingly common.