Respiratory viruses (non-influenza, non-RSV)

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.

Respiratory syncytial virus is the leading cause of bronchiolitis and infant hospitalization for lower respiratory tract infection, peaking in fall and winter in children under two years. Diagnosis is clinical; management is supportive, and prevention now centers on universal infant immunoprophylaxis with nirsevimab or maternal RSV vaccination.

COVID-19 is the respiratory illness caused by SARS-CoV-2, a positive-sense RNA coronavirus that binds ACE2 receptors, ranging from asymptomatic infection to hypoxemic pneumonia and acute respiratory distress syndrome. Diagnosis relies on RT-PCR of a nasopharyngeal sample, and hospitalized hypoxemic patients are treated with dexamethasone plus remdesivir, escalating to baricitinib or tocilizumab and thromboprophylaxis.

Acute bronchitis is a self-limited lower respiratory tract infection causing cough lasting more than five days after other upper respiratory symptoms resolve, almost always viral, and diagnosed clinically after pneumonia is excluded. Management is symptomatic; antibiotics do not shorten the illness and should be withheld absent signs of pneumonia or pertussis.

Acute rhinosinusitis is inflammation of the nasal cavity and paranasal sinuses lasting up to 4 weeks, presenting with purulent nasal discharge plus nasal obstruction or facial pain/pressure/fullness. Most cases are viral and treated with acetaminophen/ibuprofen plus nasal saline irrigation alone; a minority are bacterial, identified by persistence beyond 10 days, a biphasic worsening course, or severe onset, and treated with amoxicillin-clavulanate 875/125 mg PO every 12 hours for 5 to 7 days.

Streptococcal pharyngitis is an acute infection of the tonsils and pharynx caused by group A Streptococcus pyogenes, presenting with rapid-onset sore throat, fever, tonsillar exudates, and tender anterior cervical lymphadenopathy without cough; diagnosis relies on the Centor criteria to guide rapid antigen testing, and treatment with penicillin or amoxicillin prevents suppurative complications and acute rheumatic fever.

Acute otitis media is a suppurative middle ear infection, mostly in young children, diagnosed by otoscopy showing a bulging, erythematous tympanic membrane with an effusion, and it is treated with observation or amoxicillin depending on age and severity.

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.

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.

Conjunctivitis is inflammation of the conjunctiva from viral, bacterial, or allergic causes presenting with red eye, discharge, and preserved vision, diagnosed clinically by discharge character and managed with supportive care, targeted topical antibiotics, or topical antihistamine/mast-cell-stabilizer therapy.