The respiratory system

Taking a deep breath – this is something we do every day, all day; we don’t even think about it. It sounds really simple, but there are many organs involved for this process to work properly: nose, throat, larynx, trachea, bronchi, and lungs. All these together is what we know as the respiratory system.

The respiratory tract can be separated into:

  • Upper respiratory tract: nose, pharynx, and larynx (organs outside the thorax).
  • Lower respiratory tract: trachea, bronchi, bronchioles, alveolar duct, and the alveoli (organs within the thorax).

Upper respiratory tract infections - URTIs

Upper respiratory tract infections, short URTIs, are infections of mouth, nose, larynx, and trachea. Upper respiratory infections are mostly caused by viruses. Therefore, antibiotic prescription is most of the times unnecessary and increases the risk for antibiotic resistances.

Respiratory tract infections include


Pharyngitis & Tonsillitis

Flu (Influenza)

Common Cold



Otitis Media


Bronchitis & Tracheitis

Sympthoms of URTI

  • Common Cold
  • Flu
  • Bron­chitis
  • Covid-19
Common ColdFluBron­chitisCovid-19
Common symptomsNasal congestion (80 %
of patients)
Itchy & watery eyes
Sneezing Sore/scratchy throat
Chest discomfort and
Fever (38.9 – 40°C)
Sore throat
Chest discomfort and
General aches and
Fatigue, exhaustion
and weakness
Acute & Chronic:
Chest congestion
Productive or non-productive
Shortness of breath
Wheezing or whistling sound
when one breathes
Shortness of breath or difficulty breathing
Possible symptomsLow-grade fever
Chills Headache
General malaise
Body aches and chills
Feeling „wiped out“
Low fever Runny, stuffy nose
Sore throat
Body aches
Loss of taste or smell
Sore throat
OnsetSlowly over the course
of 1-3 days
DurationUsually ends within
7-10 days
A runny or stuffy nose
and cough can last for
up to 14 days.
Symptoms usually
end after 5-7 days.
Coughing and
malaise may persist
for 14 days or longer.
Acute: Cough can
last for a few weeks (14 days or longer)
Chronic: Cough lasts ≥ 3 months and comes back within 2 years
Duration depends on severity of illness.
Mild cases:
10-14 days
Severe cases:
symptoms may last longer
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Upper respiratory tract infections

The common cold is the most frequent human illness. An adult catches a common cold around two to three times a year, whereas children can be affected up to eight times a year.

  • The common cold is a viral infection: can be caused by members of several families of viruses, including Rhinovirus, Coronavirus, Parainfluenza, and Adenovirus.

How the common cold is transmitted

The virus can be transmitted in several ways; the droplet transmission is the most common way.

Bronchitis is when the bronchial tubes, which carry air to the lungs, get inflamed and swollen. People infected end up with a nagging cough and mucus.

  • Most often, the same viruses that give you a cold or the flu cause acute bronchitis. But sometimes, bacteria bring it on.

There are two types of bronchitis:

  • Acute bronchitis: This is more common. Symptoms last for a few weeks, but it doesn’t usually cause problems past that.
  • Chronic bronchitis: This one is more serious. It keeps coming back or doesn’t go away.

Also called the flu. It is a common but sometimes serious VIRAL infection (influenza virus – types A and B in humans) of the lungs and airways.

It can cause congestion, fever, body aches, and other symptoms.

The flu is a highly contagious infections, ranging from mild to severe and even fatal. Persons aged 65+ should be especially cautious as there are high rates of mortality and hospitalization in this age group.

Children are important drivers of influenza virus transmission in the community.

COVID-19 and influenza viruses have a similar disease presentation. They both cause respiratory disease, which presents as a wide range of illness from asymptomatic or mild through to severe disease and death.

Secondly, both viruses are transmitted by contact, droplets and fomites. As a result, the same public health measures, such as hand hygiene and good respiratory etiquette (coughing into your elbow or into a tissue and immediately disposing of the tissue), are important actions all can take to prevent infection. 


How are COVID-19 and influenza viruses different?

COVID-19 is a new type of coronavirus, emerging late in 2019. To date, the flu is more likely to appear with rapid onset of illness, high fever and prominent headache and body aches. In contrast, COVID-19 may present with slower onset of illness, mild headache and body ache and mild/absent fever.

  • Influenza has a shorter median incubation period than COVID-19 virus.
  • The serial interval for COVID-19 virus is estimated to be 5-6 days, while for influenza virus, the serial interval is 3 days. This means that influenza can spread faster than COVID-19. 
  • The reproductive number – the number of secondary infections generated from one infected individual – is understood to be between 2 and 2.5 for COVID-19 virus, higher than for influenza.

Upper respiratory tract infections in children

In the upper paragraphs we learnt that upper respiratory tract infections are likely to be caused by viruses.

The viruses that mainly cause respiratory infections in children are:

  • Rhinovirus
  • Influenza viruses
  • Parainfluenza viruses
  • Respiratory syncytial virus (RSV)
  • Enteroviruses
  • Coronaviruses
  • Certain strains of Adenovirus

Because children are not yet immune to those viruses, they are likely to get more infections than adults. In average, children will suffer from 6 viral respiratory tract infections per year. Different than in adults, children usually get infected through hand contact with nasal secretions of an infected person. When touching nose or eyes the child gets infected itself. The droplet transmission (breathing air that contains droplets, coughed or sneezed out by an infected person) is less common in children.

Signs & sympthoms of URTI in children

  • Nasal congestion
  • Temperature/Fever
  • Headaches
  • Runny nose
  • Decreased appetite
  • Body aches
  • Scratchy throat
  • Lethargy
  • Coughing
  • Malaise

Babies and small Kids:
While nasal congestion is not a big deal for adults it can be difficult for new-borns and young infants as they mainly breathe through their nose. It also can be problematic while feeding on bottle or breast. When adults cough up mucus, they simply spit it out. Infants, however, are unable to do so and therefore often gag. As a child’s airways are more narrow than an adult’s, breathing is furthermore complicated. A cool-mist vaporizer, humidifying the air, may help with nasal congestion; getting the mucus out of the nose with a rubber suction bulb might also ease the discomfort.

Upper Respiratory Tract Infections in Children​

Did you know?

Children are more likely to spread their infection to others.

The reasons for that are:

  • Nasal and respiratory secretion from infected children contains more viruses compared to infected adults.
  • Children do not pay as much attention to hygiene as adults.
  • When at school or day care centres, many children are gathered in one room, making a transmission more likely.


Usually upper respiratory tract infections in children will resolve on themselves but if your child suffers from any of the above symptoms (in this box) you should consult a doctor.
A middle ear infection or pneumonia can be caused by the virus itself or by a bacterial infection; while suffering from URTI, the body is more susceptible to other germs due to the inflammation of the virus.

  • Wheezing
  • Stridor
  • Gasping for breath
  • Cyanosis (turning blue)
  • Otitis media
  • Pneumonia