Viruses of the respiratory tract and indoor air

Many viruses of the respiratory tract, such as the coronavirus and influenza, are spread by droplet transmission and through airborne transmission of fine aerosols. Droplets and aerosols are being generated when a person who has been infected speaks, sings, coughs, sneezes, or shouts. The louder the voice, the greater the formation of both droplets and aerosols.

Droplet transmission can occur only near the infectious person. Meanwhile, aerosols can stay suspended in the air for extended periods of time,and can be transferred by air movements in open spaces, sometimes covering long distances, which can occasionally lead  to transmission at a greater distance. If ventilation is poor, aerosols can sometimes remain suspended in the air for hours. Consequently, the risk of airborne infections increases in indoor spaces with inadequate ventilation.

In everyday situations, the risk of possible airborne infections is reduced by:

• adequate ventilation
• sufficient distance between people
• using a facemask in places where many other people are present. A mask also protects the person wearing it to some degree. 
  Information on face masks, surgical masks and respirators (Finnish Institute of Occupational Health)
• limiting the number of people in the same location
• moderating the use of voice.   

In close contact respiratory tract infections can also be spread through touch for example if the infected person has coughed in his hands and later touches another person.

• Preventing respiratory tract infections
• Read more about how coronavirus Covid-19 spreads

High indoor air quality supports health and wellbeing. Efficient ventilation is also important for removal of contaminants from indoor air. There are several ways to improve the efficiency of ventilation.

How to ensure sufficient ventilation?

Ventilation must be continuous at home, for example, and in constantly occupied rooms. During occasional periods when such a space is not occupied, the ventilation may be turned down, but it should never be turned completely off.

The supply air must be outside air, and the amount of supply air should always be dimensioned according to the occupancy of the space. When there are more people than usual in the space, for example when visitors are present, ventilation can be increased either by increasing incoming air mechanically or by opening windows. The air must move from clean zones to dirty zones. At home, supply air is directed to bedrooms and from there, for example, to the kitchen and wet spaces.

Make sure that ventilating systems are working properly: adhere to the recommended filter change interval and regularly clean the ventilation ducts.

What is adequate ventilation?

In Finland, the outdoor air flow in residential homes must be at least 18 litres per second in normal circumstances, according to the Decree of the Ministry of the Environment (1009/2017). In living areas, the outdoor air flow must be at least 6 litres per second per person. For the best S1 ventilation category, the Finnish Society of Indoor Air Quality and Climate recommends 0.5 litres per square metre of floor + 10 litres per second per person.

There are some easy ways for residents themselves to evaluate the adequacy of ventilation. Indications of good ventilation are for example if a bathroom dries quickly after someone has taken a shower, if a sheet of paper stays stuck to an air vent due to effective suction, and if the indoor air has a neutral smell.

How else can I increase the effectiveness of ventilation?

If it is not possible to adjust mechanical ventilation to a sufficient level, you can air the room by opening windows for a short period of time. Creating a cross-draught is recommended, if weather permits (and by taking into account the possible pollen or street dust season).

How should I clean my home to prevent infections?

In homes, the same instructions apply to the prevention of respiratory tract infections as with other infectious diseases: clean up well after yourself and avoid, for example, the use of shared towels.

All frequently touched surfaces, such as door handles, armrests, tabletops, light switches, and water taps, should be thoroughly cleaned. A mildly alkaline all-purpose detergent can be used for cleaning at home.