Three common preventable infectious respiratory diseases are:

Three common preventable infectious respiratory diseases	Coronavirus disease 2019 (COVID-19)	Influenza (Flu)	Pneumococcal Infection
Definition	COVID-19 caused by a new coronavirus called Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2)	Acute respiratory illnesses caused by influenza virus	Mostly refers to illnesses caused by Streptococcus pneumoniae (or pneumococcus)
Pathogens	Alpha - B.1.1.7 Beta - B.1.351 Gamma - P.1 Delta - B.1.617.2 Omicron - B.1.1.529	Type A - H1N1 (pdm09) & (H3N2) Type B Type C	Over 90 serotypes of Streptococcus pneumoniae

2.1. Coronavirus disease 2019 (COVID-19)

The first local case was confirmed on 23 January 2020 and there have been five waves of outbreaks since then.

According to the statistics of the Department of Health, as of 29 January 2023, there were a cumulative total of 1,226,467 cases with positive SARS-CoV-2 nucleic acid test results and 1,880,112 cases with positive rapid antigen test results in Hong Kong, representing an incidence rate of 25.4%.

2.2. Influenza

• In Hong Kong, influenza is most common in winter (January to March) and summer (July to August).
• According to the World Health Organization, the prevalence of influenza worldwide is estimated to be 5-10% in adults and 20-30% in children. It causes respiratory problems leading to death cases between 290,000 and 650,000 each year.
• According to the Centre for Health Protection (CHP), as of 4 November 2023, there were 21,988 influenza cases.

2.3. Pneumococcal Infections

• Diseases caused by Streptococcus pneumoniae occur monthly.
• The peak season for the disease is from winter to spring.
• According to the data from the Centre for Health Protection (CHP), a total of 492 pneumococcal infections were recorded in Hong Kong from 2018 to March 2023.
• The incidence of invasive pneumococcal disease in Hong Kong ranged from 0.34 to 2.54 per 100,000 persons, with higher incidence rates in people aged 2-4 and aged 65 and above.

4.1. Coronavirus disease 2019

According to the BMJ, the time of onset for COVID-19 complications is varied. The likelihood and susceptible populations of complications are shown in the following table:

According to the World Health Organization (WHO), complications of COVID-19 may lead to death. These complications may include: respiratory failure, acute respiratory distress syndrome, sepsis and septic shock, thromboembolism and/or multi-organ failure, including the heart, liver or a kidney injury.

4.2. Influenza

Influenza complications are less common but can occur occasionally. The complications include pneumonia, worsening of respiratory symptoms in patients with asthma or Chronic obstructive pulmonary disease, secondary bacterial infections, and heat cramps in young children. Rare but fatal complications: inflammation of the heart muscle (myocarditis), inflammation of the brain tissue (encephalitis), and inflammation of the peripheral nerves (Guillain-Barre syndrome).

4.3. Pneumococcal infections

Pneumococcus can cause different types of diseases; more common ones are pneumonia and otitis media. It can lead to invasive pneumococcal disease resulting in a serious or even fatal condition.

Symptoms depend on the site of infection:

• Otitis media: The infection can present with fever, ear pain and sometimes with discharge. It may lead to hearing loss in recurrent infection.
• Pneumonia: There may be shortness of breath, fever, cough with phlegm and chills; death may occur in severe cases.
• Meningitis: Neck stiffness, fever and confusion may occur. It may result in long-term hearing loss or even death.
• Sepsis and bacteremia: There may be chills and joint pains, and there may be concurrent infections in other parts of the body, e.g., meningitis and pneumonia.

Anyone can get sick, become seriously ill or die from the above three common preventable infectious respiratory diseases!

8.1 Modes of transmission

• Three infectious respiratory diseases virus can transmit via droplets from the respiratory tract (within 2 meters), touching the surfaces or objects contaminated with the virus.
• COVID-19 can spread via short distance aerosols* or airborne transmission. The virus may also be transmitted in poorly ventilated and/or crowded indoor environments.
• Incubation period are estimated to be 1 to 14 days for COVID-19. Some variants may have a shorter incubation period#, such as the Omicron variant, which has an incubation period of about 3 days.
• An infected person can be contagious and can transmit the virus to others, regardless of whether they have the disease or not.

*Aerosols is one form of airborne transmissions, but airborne transmission is not necessarily via aerosols. Its size is around 5 to 10 microns and can float in the air from a few minutes to a few hours, and at a distance of up to around 10 meters. Aerosol transmission usually takes place in confined environments (e.g., in lifts, cruises).
#The incubation period is the time between an infection and the onset of clinical symptoms of the disease.

8.2. Viral infection detection methods