What are respiratory infections?

Respiratory infections are infectious diseases of the respiratory tract that are mostly caused by bacteria and viruses. They cause infections of the throat, sinuses, airway path, and lungs. Respiratory infections are typically divided into two types: upper tract respiratory infection and lower tract respiratory infection.


Respiration is a metabolic process that occurs in all living organisms. In this process, the intake of oxygen occurs with the release of carbon dioxide due to the oxidation of complex organic substances (glucose). Any infection of the respiratory tract hinders the process of respiration.

Acute respiratory infections

Acute respiratory infection interferes with the normal respiration process and causes difficulty in breathing. It can affect both the upper respiratory tract and the lower respiratory tract. Its symptoms include sore throat, body ache, fever, fatigue, runny nose, and so on. Up to 15% of infections are caused by bacteria such as Streptococcus pyogenes.

Manifestations of upper respiratory acute infection include acute pharyngitis, acute ear infection, and the common cold. Manifestations of lower respiratory infection include bronchitis and pneumonia. Anyone with low immunity, due to any underlying disease or with heart disease, is highly prone to acute respiratory infections.

Acute respiratory infections if not treated properly in time can lead to permanent damage of lungs or even death. The complications include respiratory arrest, which occurs when the lungs stop functioning, a rise in CO2 (carbon-di-oxide) in your blood, and congestive heart failure.

Types of respiratory infections

Differentiating anatomically the upper and lower respiratory tract.

CC-PD-Mark | Image credits: https://commons.wikimedia.org | Lord_Akryl & Jmarchn

Upper respiratory tract infections

The upper respiratory infections occur above the glottis (vocal cords) area of the respiratory tract or up to the cricoid cartilage (cartilage which circularly covers the trachea and supports the muscles, ligaments by providing an attachment site). The upper respiratory tract includes the nose, tracheae, sinuses, larynx, and pharynx. The upper respiratory tract infection includes tonsillitis, pharyngitis, laryngitis, sinusitis, otitis media, certain influenza types, and the common cold. These are mostly bacterial infections. The common symptoms are cough, sore throat, runny nose, nasal congestion, high fever, and headache.


It is the inflammation of the upper part of the throat, the tonsils. The symptom includes sore throat, enlargement of tonsils, difficulty in swallowing, and fever. It can be a viral infection or bacterial infection, usually caused by the bacterium Group A streptococcus. This infection spread through air droplets. Proper medicines can be used to treat symptoms along with a course of antibiotics.


It is the inflammation of the pharynx, a portion present at the back of the throat, and it brings about sore throat and fever. Other symptoms may include swollen pharynx, difficulty in swallowing, and hoarse voice. Streptococcal pharyngitis is caused by Group A beta-hemolytic Streptococcus. It is treated with antibiotics such as penicillin and amoxicillin.


Sinusitis is the inflammation of the lining of sinuses, which is the mucous membrane. The symptoms include plugged nose, sore throat, poor sense of smell, facial pain, thick nasal mucous, headaches, and fever. It is a viral infection and generally lasts less than 4 weeks. Sinusitis may also occur due to infections, allergies, air pollution, or structural problems of the nose. Painkillers such as naproxen, nasal steroids may help. Acute sinusitis is generally of the viral origin, mostly caused by rhinovirus. If it is one of the bacterial infections, a bacterium named Streptococcus pneumoniae is responsible for causing sinusitis.

Common cold

It is a viral infection, and primarily affects the mucosa layer of the nose, sinus, throat. The symptoms include sore throat, cough, running nose, fever, headaches. This does not require any special treatment, over-the-counter medicine will work. Over 200 virus strains are known to cause the common cold. The most common are rhinoviruses, coronaviruses, adenoviruses, and enteroviruses.


It is commonly called the 'flu'. The symptoms often include fever, runny nose, sore throat, headache, coughing, and fatigue. These symptoms typically last for about 2–8 days. Pneumonia can be caused by the primary viral infection or by a secondary bacterial infection, a recurring or progressive condition of Influenza. There are four types of influenza viruses; A, B, C, and D. Influenza-like illness is a diagnosis of possible influenza or other disease-causing the same set of symptoms.

All these diseases including bronchiolitis, common cold, influenza are viral respiratory infections.

Lower respiratory tract infections

Based on the severity; lower respiratory tract infections are fatal than upper respiratory tract infections. The lower respiratory tract includes the trachea, bronchioles, bronchial tubes, and lungs. The most common lower respiratory tract infections are bronchitis and pneumonia.


It is inflammation of the bronchi, the airways in the lungs, that causes coughing. The symptoms include coughing up sputum, wheezing, shortness of breath, and chest pain. Bronchitis can be acute or chronic.

Acute bronchitis usually has a cough, and it may last around three to four weeks. Mostly, the cause is a viral infection that can spread through direct contact or air droplets. In some cases, it is caused by the bacterium Mycoplasma pneumoniae or Bordetella pertussis. A proper amount of rest, paracetamol, or other anti-inflammatory drugs can work as a treatment medication for acute bronchitis.

Chronic bronchitis is a productive cough in which one produces sputum that lasts for three months or more for at least two years. Many people with chronic bronchitis also have chronic obstructive pulmonary disease (COPD). Tobacco smoking is the most common cause. Treatment of bronchitis includes quitting smoking, vaccinations, rehabilitation, and often inhaled bronchodilators and steroids.


It causes the inflammation of small air sacs present within the lungs called alveoli, which are liable for the exchange of gases. The symptom may include pain, fever, productive or dry cough, and difficulty in breathing. Pneumonia may be caused by either bacteria or viruses. The pneumonia-causing bacterium is Streptococcus pneumoniae and is the leading cause of pneumonia. Bacterial pneumonia is the leading cause of morbidity and mortality as well. Some others are human rhinovirus and influenza virus. There could be two possibilities of this infectious disease; either hospital-acquired pneumonia or community-acquired pneumonia.

Parainfluenza Viruses

Parainfluenza viruses are a group of viruses called the Human Parainfluenza virus (HPV). These are groups of four viruses; HPV1, HPV2, HPV3, and HPV4. The symptoms of HPV are the same as the common cold. Most people recover on their own and do not require any treatment. People with weakened immune systems need treatment and, if not given properly, are at risk of developing a life-threatening infection.


Coronavirus-19 (Covid-19) is a highly infectious disease caused by severe acute respiratory syndrome coronavirus- 2 (SARS-CoV-2). The foremost common complication of severe COVID-19 is acute respiratory failure, according to acute respiratory distress syndrome. COVID-19 affects the airway, lungs, pulmonary, and neuromuscular pathways. The symptoms of COVID-19 include fever, cough, headache, fatigue, breathing difficulties, and loss of smell and taste. Symptoms begin between 1 and 14 days after exposure to the virus. Many people exposed to the virus do not develop noticeable symptoms and are mentioned as asymptomatic patients. COVID-19 contracts when people inhale air contaminated by droplets and little airborne particles or touch an infected area. The danger of breathing in the virus is higher when people are in close proximity, so practicing social distancing is advised. The cool-mist humidifiers prevent the spread of this respiratory disease in close contact, such as the ones kept at home or in hospitals. The precaution for such disease is to maintain social distancing, regular and proper hand wash habits, use alcohol-based sanitizer, and a healthy lifestyle and diet.

Context and applications

This topic holds relevance to many undergraduates as well as postgraduate courses. It is included in courses such as

  • Anatomy and Physiology
  • Pathology
  • Pathophysiology
  • Medicine
  • Pharmacy.

Practice problems

1. Which respiratory disease is characterized by blocked airway passage and constriction?

  1. Chronic bronchitis
  2. Pneumonia
  3. Asthma
  4. Common cold

Answer: c

Explanation: Asthma is the condition in which the airway passage becomes narrow and swell, causing shortness of breath.

2. How many virus strains are known to cause the common cold?

  1. 100
  2. 200
  3. 300
  4. 400

Answer: b

Explanation: Over 200 strains of viruses are known to cause the common cold.

 3. For how many hours, COVID-19 virus can be active on a surface?

  1. 5-6 hours
  2. 2-3 hours
  3. 10-12 hours
  4. 15-20 hours.

Answer: c

Explanation: Covid-19 virus can survive on surfaces for up to 10-20 hours, therefore disinfectants are recommended.

  1. Which of the following disease can be cured by penicillin and amoxicillin?
  1. Laryngitis
  2. Influenza
  3. Bronchitis
  4. Pharyngitis

Answer: d

Explanation: Pharyngitis is the inflammation of the pharynx which brings about sore throat and can be cured by taking antibiotics.

  1. What is cricoid cartilage?
  1. Cartilage circularly covering the tracheae
  2. The matrix surrounding the trachea
  3. Cartilage transversely covering the larynx
  4. Cartilage horizontally covering the trachea

Answer: a

Explanation: Cricoid cartilage is cartilage covering the trachea circularly and supports the muscles also providing a site for attachment.

Common Mistakes

Often, pneumonia is mistaken with tuberculosis. Tuberculosis is a contagious infection caused by bacteria that mainly affects the lungs, but it also affects other organs such as bone, brain, and spine. While pneumonia is an inflammatory disease of the lungs that can be caused by bacteria as well as viruses. But, if pneumonia is caused by the bacteria Mycobacterium tuberculosis, it will eventually lead to tuberculosis.

  • Respiration
  • Covid-19
  • Respiratory tract infections

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