Common Viral Respiratory Infections, Other Than COVID-19¶
Chapter 204 | Part 5: Infectious Diseases
KEY CLINICAL POINTS¶
- Respiratory viruses include influenza, RSV, hMPV, rhinoviruses, adenoviruses, and coronaviruses, with distinct clinical presentations and transmission patterns.
- Influenza A and B viruses cause seasonal epidemics, while RSV and hMPV are major causes of severe lower respiratory tract disease in infants and elderly.
- Antiviral therapies like oseltamivir, zanamivir, and baloxavir are effective for influenza, while ribavirin and intravenous cidofovir are used for severe RSV/hMPV infections.
- Vaccination is critical for prevention, with trivalent/quadrivalent influenza vaccines and RSV vaccines (Arexy/Abrysvo) available for high-risk populations.
- Special considerations include immune-mediated complications, nosocomial transmission, and the role of immunocompromised hosts in viral pathogenesis.
1. DEFINITION & OVERVIEW¶
Common viral respiratory infections encompass a wide range of pathogens affecting the upper and lower respiratory tracts. These infections range from mild (common cold) to severe (pneumonia, ARDS) and are caused by diverse viruses including influenza, respiratory syncytial virus (RSV), human metapneumovirus (hMPV), rhinoviruses, adenoviruses, and coronaviruses. The clinical manifestations vary by viral type and host factors, with significant morbidity and mortality in vulnerable populations.
Table 203-1: Recommended Treatments for Genital Warts Caused by HPV¶
| TREATMENT | EFFECTIVENESS | ADVERSE EFFECTS | COST |
|---|---|---|---|
| IMIQUIMOD | Good | Frequent, mild to moderate | Expensive |
| CRYOTHERAPY | Good | Mild, well tolerated | Inexpensive |
| INTERFERON | Good | Frequent, moderately severe | Very expensive |
| SURGICAL REMOVAL | Excellent | Mild, well tolerated | Moderately expensive |
| LASER | Excellent | Mild to moderate, well tolerated | Very expensive |
1.1 Viral Classification¶
Viruses are categorized by family (e.g., Orthomyxoviridae for influenza, Paramyxoviridae for RSV/hMPV, Picornaviridae for rhinoviruses), with distinct replication strategies and pathogenic mechanisms. Coronaviruses (e.g., SARS-CoV, MERS-CoV) and parvoviruses (e.g., HBoV) also contribute to respiratory disease.
1.2 Clinical Spectrum¶
Infections range from asymptomatic carriage to severe pneumonia. Upper respiratory tract infections (common cold, pharyngitis) are more common in children, while lower respiratory tract disease (bronchiolitis, pneumonia) is prevalent in infants, elderly, and immunocompromised patients.
2. EPIDEMIOLOGY¶
Respiratory viruses exhibit seasonal and geographic variation, with influenza and RSV causing annual epidemics. RSV peaks in winter, while influenza has bimodal seasonal patterns. Global incidence varies, with higher rates in temperate regions. Risk factors include age (infants, elderly), immunocompromised status, and comorbidities (COPD, asthma).
Table 204-1: Family Pneumoviridae Human Pathogens¶
| GENUS | CURRENT SPECIES | FORMER SPECIES NAME(S) |
|---|---|---|
| Metapneumovirus | Metapneumovirus hominis (hMPV) | Human metapneumovirus |
| Orthorubulavirus | Human orthorubulavirus | Mumps virus, Parainfluenza virus |
2.1 Seasonality¶
Influenza and RSV infections are most common in winter (November–March in the Northern Hemisphere), while coronaviruses (e.g., SARS-CoV-2) show less seasonal variation. Tropical regions have year-round transmission with peak activity during rainy seasons.
2.2 Transmission¶
Primary transmission occurs via respiratory droplets and fomites. Small-particle aerosols ( ≤ 5 µ m) contribute to airborne spread for certain pathogens (e.g., measles, tuberculosis). Close contact in healthcare settings or crowded environments increases transmission risk.
3. ETIOLOGY & PATHOPHYSIOLOGY¶
Viruses exploit host cell receptors (e.g., ACE2 for SARS-CoV-2, CD150 for RSV) to initiate infection. Pathogenesis involves viral replication, immune evasion, and host inflammatory responses. For example, RSV induces bronchiolar inflammation and mucus hypersecretion, while influenza viruses cause epithelial damage and cytokine storm.
Table 204-2: Paramyxoviridae Human Pathogens¶
| GENUS | CURRENT SPECIES | FORMER SPECIES NAME(S) |
|---|---|---|
| Respirovirus | Human respirovirus 1 (hPIV1) | Parainfluenza virus type 1 |
| Orthorubulavirus | Human orthorubulavirus | Mumps virus, Parainfluenza virus |
3.1 Viral Mechanisms¶
Viruses use specific receptors (e.g., sialic acid for influenza, integrins for adenovirus) to enter host cells. Some viruses (e.g., measles) replicate in the bloodstream, while others (e.g., rhinoviruses) remain localized to the upper respiratory tract.
3.2 Immune Evasion¶
Viruses evade innate immunity through mechanisms like inhibition of interferon production (RSV) or antigenic drift (influenza). Immunocompromised hosts are at higher risk for persistent infections and severe disease.
4. CLINICAL FEATURES¶
Symptoms vary by viral type: common cold (rhinorrhea, sore throat), influenza (fever, myalgia), RSV (wheezing, pneumonia), and measles (rash, Koplik spots). Severe disease is more common in infants, elderly, and immunocompromised patients, with complications like bacterial superinfections or ARDS.
Table 204-3: Enterovirus, Rhinovirus, and Parechovirus Species¶
| GENUS | CURRENT SPECIES | FORMER SPECIES NAME(S) |
|---|---|---|
| Enterovirus | Human enterovirus A | Coxsackievirus, Echovirus |
| Rhinovirus | Human rhinovirus A | Rhinovirus species |
| Parechovirus | Human parechovirus 1 (HPeV-1) | Parechovirus A |
4.1 Common Cold¶
Mild symptoms include rhinorrhea, sneezing, and sore throat. Rhinoviruses are the most common cause, with seasonal variation. Complications include otitis media in children and sinusitis in adults.
4.2 Severe Lower Respiratory Tract Disease¶
RSV and hMPV cause bronchiolitis and pneumonia in infants, while influenza can lead to ARDS. Symptoms include tachypnea, cyanosis, and respiratory failure requiring mechanical ventilation.
5. DIFFERENTIAL DIAGNOSIS¶
Differential diagnosis includes bacterial infections (e.g., streptococcal pharyngitis), atypical pathogens (e.g., Mycoplasma), and non-infectious causes (e.g., asthma exacerbations). Viral vs. bacterial etiology is distinguished by clinical presentation, epidemiology, and diagnostic testing.
5.1 Upper Respiratory Tract¶
Common cold vs. bacterial pharyngitis: rhinovirus vs. Streptococcus pyogenes. Measles vs. scarlet fever: Koplik spots vs. strawberry tongue.
5.2 Lower Respiratory Tract¶
RSV pneumonia vs. bacterial pneumonia: wheezing vs. crackles, viral vs. bacterial etiology on imaging and culture.
6. INVESTIGATIONS & DIAGNOSIS¶
Diagnostic methods include RT-PCR for viral RNA detection, rapid antigen tests, and viral culture. Imaging (chest X-ray) helps assess pneumonia severity. Serologic testing and molecular assays (e.g., multiplex panels) identify co-infections or emerging pathogens.
Table 204-1: Family Pneumoviridae Human Pathogens¶
| GENUS | CURRENT SPECIES | FORMER SPECIES NAME(S) |
|---|---|---|
| Metapneumovirus | Metapneumovirus hominis (hMPV) | Human metapneumovirus |
| GENUS | CURRENT SPECIES | FORMER SPECIES NAME(S) |
|---|---|---|
| Orthorubulavirus | Human orthorubulavirus | Mumps virus, Parainfluenza virus |
6.1 Diagnostic Tests¶
RT-PCR is the gold standard for detecting viral RNA in respiratory secretions. Rapid antigen tests (e.g., for influenza, RSV) are less sensitive but provide quick results. Viral culture is used for research or resistant strains.
6.2 Imaging¶
Chest radiography is essential for diagnosing pneumonia. CT scans may be used in severe cases or for evaluating complications like pulmonary edema.
7. MANAGEMENT & TREATMENT¶
Management is primarily supportive, with antiviral agents (oseltamivir, zanamivir) for influenza and ribavirin for severe RSV/hMPV. Immunocompromised patients may require intravenous antivirals (e.g., cidofovir). Prevention includes vaccination and passive immunization (palivizumab for RSV).
Table 204-1: Family Pneumoviridae Human Pathogens¶
| GENUS | CURRENT SPECIES | FORMER SPECIES NAME(S) |
|---|---|---|
| Metapneumovirus | Metapneumovirus hominis (hMPV) | Human metapneumovirus |
| Orthorubulavirus | Human orthorubulavirus | Mumps virus, Parainfluenza virus |
7.1 Antiviral Therapy¶
Neuraminidase inhibitors (oseltamivir, zanamivir) are effective for influenza. Ribavirin is used for severe RSV/hMPV, while baloxavir targets viral endonuclease. Intravenous cidofovir is reserved for adenovirus infections.
7.2 Supportive Care¶
Oxygen therapy, hydration, and bronchodilators are critical for severe cases. Mechanical ventilation may be required for ARDS. Monitoring for secondary bacterial infections is essential.
8. PROGNOSIS & COMPLICATIONS¶
Prognosis varies by virus and host factors. Most viral infections are self-limiting, but severe cases (e.g., RSV pneumonia, influenza ARDS) can lead to long-term respiratory impairment or mortality. Complications include bacterial superinfections, secondary infections, and immune-mediated damage.
8.1 Mortality¶
Influenza mortality is highest in elderly and immunocompromised patients. RSV-related deaths are most common in infants <1 year old. Severe cases of hMPV and adenovirus infections also carry significant mortality.
8.2 Long-Term Effects¶
RSV infection in infancy is associated with increased risk of asthma. Chronic bronchitis and COPD exacerbations are common in adults with recurrent viral infections.
9. SPECIAL CONSIDERATIONS¶
Pregnancy, pediatric, and geriatric populations require tailored management. Immunocompromised patients (e.g., transplant recipients) are at higher risk for severe disease and opportunistic infections. Nosocomial transmission in healthcare settings necessitates strict infection control measures.
Table 204-1: Family Pneumoviridae Human Pathogens¶
| GENUS | CURRENT SPECIES | FORMER SPECIES NAME(S) |
|---|---|---|
| Metapneumovirus | Metapneumovirus hominis (hMPV) | Human metapneumovirus |
| Orthorubulavirus | Human orthorubulavirus | Mumps virus, Parainfluenza virus |
9.1 Pregnancy¶
Influenza vaccination is recommended for pregnant women to prevent maternal and fetal complications. RSV infection in late pregnancy may increase risk of preterm birth.
9.2 Immunocompromised Hosts¶
CMV, EBV, and herpesviruses can cause severe disease in transplant recipients. Antiviral prophylaxis (e.g., ganciclovir for CMV) is critical in high-risk patients.
10. KEY POINTS & CLINICAL PEARLS¶
- Use RT-PCR for rapid viral identification in respiratory infections. 2. Vaccinate high-risk populations (elderly, infants, immunocompromised) against influenza and RSV. 3. Antiviral therapy is most effective when initiated early in influenza. 4. Monitor for bacterial superinfections in viral pneumonia. 5. Implement strict infection control measures in healthcare settings to prevent nosocomial transmission.