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  second-hand smoke exposure , indoor dampness and mould , and outdoor air pollution  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 . 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 2021, there were 9422 LRTI hospitalisations in children under five years old, up from 2852 in 2020. When compared with the last year prior to the COVID-19 pandemic, LRTI hospitalisations in 2021 were five percent lower (518 hospitalisations) than in 2019 (Figure 1).
Figure 1: Number of lower respiratory tract infection hospitalisations in children aged 0–4 years, 2001–2021
Usual winter LRTI hospitalisation peak returned in 2021
The number of LRTI hospitalisations rebounded quite quickly in New Zealand and overseas following the easing of COVID-19 restrictions. There was a surge in LRTI hospitalisations during the 2021 winter season, surpassing pre-pandemic trends (Figure 2). There were 3832 LRTI hospitalisations in July 2022, up from 274 in 2020, 1726 in 2019, and 1694 in 2018. 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 .
Figure 2: Number of lower respiratory tract infection hospitalisations in children aged 0–4 years, by month, 2018–20
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.
1. Baker MG, McDonald A, Zhang J, Howden-Chapman P. 2013. Infectious diseases attributable to household crowding in New Zealand: A systematic review and burden of disease estimate. Wellington: He Kainga Oranga/ Housing and Health Research Programme, University of Otago.
2. U.S. Department of Health and Human Services. 2007. Children and Secondhand Smoke Exposure. Excerpts from The Health Consequences of Involuntary Exposure to Tobacco Smoke: A Report of the Surgeon General. Atlanta, GA: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, Coordinating Center for Health Promotion, National Center for Chronic Disease Prevention and Health Promotion, Office on Smoking and Health.
3. Fisk W, Eliseeva E, Mendell M. 2010. Association of residential dampness and mold with respiratory tract infections and bronchitis: a meta-analysis. Environmental Health 9(1): 72. doi: 10.1186/1476-069X-9-72
4. Mehta S, Shin H, Burnett R, et al. 2013. Ambient particulate air pollution and acute lower respiratory infections: a systematic review and implications for estimating the global burden of disease. Air Qual Atmos Health 6: 69–83.
5. Trenholme AA, Byrnes CA, McBride C, et al. 2013. Respiratory health outcomes 1 year after admission with severe lower respiratory tract infection. Pediatric Pulmonology 48: 772–79
6. Britton PN, Hu N, Saravanos G, et al. 2020. COVID-19 public health measures and respiratory syncytial virus. Lancet Child Adolesc Health 4 (11): e42–e43.
7. Groves HE, Piche-Renaud PP, Peci A, et al. 2021. The impact of the COVID-19 pandemic on influenza, respiratory syncytial virus, and other seasonal respiratory virus circulation in Canada: A population-based study. The Lancet Regional Health – Americas 1: doi: 10.1186/1476-069X-9-72
8. Hatter L, Eathorne A, Hills T, Bruce P, Beasley R. 2021. Respiratory syncytial virus: paying the immunity debt with interest. Lancet Child Adolesc Health 5 (12): e44-e45.