Lower respiratory tract infections

Poor indoor and outdoor air quality increases the risk of lower respiratory tract infections among children

Lower respiratory tract infections (LRTI) refer to infections of the windpipe (trachea), lungs, and airways (bronchi, bronchioles). These include pneumonia, bronchitis and bronchiolitis. Household crowding [1] second-hand smoke exposure [2], indoor dampness and mould [3], and outdoor air pollution [4] increase the risk of lower respiratory tract infections in young children.

LRTI is responsible for a large burden of avoidable mortality and morbidity among young children under five years old globally. Compared with other developed countries, New Zealand has high rates of LRTI hospitalisation among young children [5]. Each year, a small number of children in New Zealand die from lower respiratory tract infections. Between 2001 and 2018, 173 children under five years of age died from lower respiratory tract infections, an average of 10 deaths every year.

The COVID-19 pandemic

Throughout 2020 and 2021 the New Zealand Government pursued an elimination strategy for COVID-19. A four-level COVID-19 alert system was in place from March 2020 to December 2021. Measures used in the system included temporary border closures, quarantine requirements, community testing, school closures, contact tracing, and lockdowns. A full national Level 4 lockdown was in place from 25 March 2020 to 27 April 2020 followed by Level 3 and Level 2 restrictions throughout much of the 2020 winter cold and flu season. 

In 2021 the only full national Level 4 lockdown was between 17 August 2021 and 31 August 2021. Outside of this period, regional Level 4 and 3 restrictions were used (particularly in the Auckland region), but lower level restrictions were in place for much of the cold and flu season across the country.

Number of LRTI hospitalisations returned to pre-Covid-19 levels after a drop in 2020

In 2022, there were 9968 LRTI hospitalisations in children under five years old, up from 9415 in 2021. This demonstrates a threefold rise in hospitalisations since the COVID-19 pandemic in 2020 (Figure 1).

Figure 1: Number of lower respiratory tract infection hospitalisations in children aged 0–4 years, 2001–2022

Usual winter LRTI hospitalisation peak returned in 2021 but remained high throughout the rest of 2022

LRTI hospitalisations during the 2022 winter season have reverted to pre-COVID-19 levels. Nevertheless, they remained notably high for the rest of the year compared to the levels observed in 2019. 

It is thought that one driver of the higher LRTI hospitalisations in 2021 was lower than usual levels of immunity among young children to respiratory syncytial virus (RSV) due to the reduced incidence of RSV and other seasonal viruses in 2020 [6,7]. Border changes in April 2021 allowed quarantine-free travel between New Zealand and Australia and RSV cases quickly increased, peaking in July 2021 [8].

Figure 2: Number of lower respiratory tract infection hospitalisations in children aged 0–4 years, by month, 2019–2022

Information about this data

Lower respiratory tract infection hospitalisations

Source: National Minimum Dataset, Ministry of Health

Definition: Acute and semi-acute hospitalisations with pneumonia (ICD-10AM J12–J16, J18), bronchitis (J20), bronchiolitis (J21) or unspecified acute lower respiratory tract infection (J22) as the primary diagnosis, for children aged 0–4 years.  Analyses excluded overseas visitors and transfers within and between hospitals. Rates have been presented per 100,000 children.