What Causes Upper Respiratory Infection?

An upper respiratory infection (URI) affects the nose, sinuses, throat and airways. It’s one of the most common illnesses worldwide, often called the “common cold.” While uncomfortable, most URIs resolve on their own within a week or two. Understanding the causes can help you prevent and manage symptoms more effectively.

Common Viral Causes

Viruses are responsible for up to 90% of all upper respiratory infections. Key pathogens include:

• Rhinoviruses
  • Account for 30–50% of URIs (Heikkinen & Järvinen, 2003).
  • Thrive in cooler nasal passages.
  • Spread by droplet inhalation or direct contact with contaminated surfaces.

• Coronaviruses
  • Cause about 10–15% of common colds.
  • Transmit via respiratory droplets and surface contact.
  • Some strains lead to more severe illness (e.g., SARS-CoV, MERS-CoV, SARS-CoV-2).

• Influenza viruses
  • Responsible for seasonal flu outbreaks.
  • May invade both upper and lower respiratory tracts.
  • Symptoms often more intense than typical colds.

• Respiratory syncytial virus (RSV)
  • Common in infants and older adults.
  • Can lead to serious lower respiratory issues in high-risk groups.

• Parainfluenza viruses
  • Cause croup in young children.
  • Spread in childcare and school settings.

• Adenoviruses
  • Associated with sore throat, fever and pink eye.
  • May survive for long periods on surfaces.

According to Zhang et al. (2013), in adult patients with acute respiratory symptoms, rhinovirus and influenza A were among the most frequently detected pathogens. Viral URIs often overlap in timing and presentation, making specific identification challenging without laboratory tests.

Less Common Bacterial Causes

Though rare, bacteria can also trigger upper respiratory infections, especially when a viral cold leads to bacterial overgrowth. Examples include:

• Streptococcus pyogenes (Group A strep)
• Haemophilus influenzae (non-typeable strains)
• Moraxella catarrhalis

Bacterial URIs commonly follow an initial viral infection and may require antibiotics if symptoms persist beyond 10 days, worsen after initial improvement, or include high fever and facial pain.

How Infections Spread

Respiratory infections move quickly through populations. Primary routes include:

• Airborne droplets
  • Coughing, sneezing or talking releases virus-laden droplets.
  • Nearby people inhale or come into contact with these droplets.

• Direct contact
  • Touching a sick person’s hands, doorknobs or shared objects.
  • Then touching your nose, mouth or eyes transfers the virus.

• Self-inoculation
  • Rubbing or scratching your face after touching contaminated surfaces.

Because many viruses survive on surfaces for hours to days, frequent hand-washing and avoiding close contact with sick individuals are crucial preventive steps.

Risk Factors and Predisposing Conditions

While anyone can develop a URI, certain factors increase susceptibility:

• Season
  • Colder months drive people indoors, raising transmission risk.
  • Low humidity helps viruses survive longer in the air.

• Age
  • Children under 6 have immature immune systems and high exposure in schools/daycare.
  • Older adults may have weaker immune defenses.

• Chronic medical conditions
  • Asthma, diabetes or heart disease can worsen URI outcomes.
  • Allergies and sinus issues may mimic or exacerbate symptoms.

• Smoking and air pollution
  • Irritate airway linings, making infections more likely and severe.

• Stress and fatigue
  • Lowered immune function increases risk of infection.

• Close quarters
  • Crowded living environments (e.g., dorms, military barracks) facilitate rapid spread.

Symptoms of Upper Respiratory Infection

Typical URI symptoms include:

• Runny or stuffy nose
• Sore or scratchy throat
• Sneezing and mild coughing
• Low-grade fever (more common in children)
• Headache or mild body aches
• Watery eyes
• Fatigue

Most symptoms peak around days 2–3 and improve by days 5–7. If symptoms linger beyond 10 days, worsen after initial improvement, or include:

• High fever (>102°F / 39°C)
• Severe headache or facial pain
• Shortness of breath
• Wheezing or chest tightness
• Confusion or persistent vomiting

you should seek medical evaluation promptly.

Preventive Measures

Stopping the spread of respiratory infection hinges on good habits:

• Wash hands frequently with soap and water for at least 20 seconds.
• Use alcohol-based hand sanitizers when soap isn’t available.
• Avoid touching your face, especially eyes, nose and mouth.
• Cover coughs and sneezes with a tissue or your elbow.
• Disinfect high-touch surfaces daily (e.g., doorknobs, light switches).
• Stay home when you’re sick to prevent passing the virus to others.
• Maintain a healthy lifestyle—balanced diet, regular exercise, adequate sleep and stress management.

Vaccines and Treatments

While there’s no universal vaccine for all cold-causing viruses, some key vaccinations include:

• Influenza vaccine (annual)
• COVID-19 vaccines (for eligible individuals)
• Pertussis (whooping cough) booster
• Pneumococcal vaccine (for older adults and high-risk groups)

Treatment for most URIs focuses on relieving symptoms:

• Rest and stay hydrated.
• Over-the-counter pain relievers (acetaminophen, ibuprofen).
• Decongestants or saline nasal sprays.
• Lozenges or throat sprays for sore throat relief.
• Humidifiers to ease nasal congestion.

Antibiotics are not effective against viruses and should only be used when a bacterial infection is confirmed by your healthcare provider.

When to Get Professional Help

Most upper respiratory infections clear up without medical intervention. However, consider speaking to a healthcare professional if you experience:

• Symptoms lasting longer than 10 days
• High or persistent fever
• Severe headache or facial swelling
• Difficulty breathing or chest pain
• Signs of dehydration (e.g., dark urine, lightheadedness)
• Worsening of chronic conditions (e.g., asthma flare-ups)

You might also consider doing a free, online symptom check for respiratory infection to guide your next steps and determine if you need in-person care.

Most importantly, always speak to a doctor about anything that could be life threatening or serious.