Discussion
COVID-19 nearly erased bronchiolitis and RSV infections within our emergency department during the first year of the pandemic, with over 80% reduction in bronchiolitis visits from the year prior. While all ED visits fell, the proportion of visits due to bronchiolitis also decreased. The marked decline in respiratory illness is likely multi-factorial and is hypothesized to be largely driven by social distancing, hand hygiene, masking, and Stay at Home Orders [11]. This trend was also noted in other parts of the world including Belgium, New Zealand, Brazil, France, and the US [12-15]. While other studies have focused on ICU patients or all cause ED visits, this study adds detailed information with a large cohort of bronchiolitis ED visits in the Southeastern US with measures of resource utilization and changes in virology as cases of bronchiolitis fell dramatically and then rose sharply.
The 2014 AAP Guidelines for the management of bronchiolitis recommends against routine chest radiographs and albuterol use [1]. Despite this, over use still occurs in many hospitals. The pandemic brought about many changes in how respiratory illnesses were acutely managed due to the novelty of COVID-19 and fears that it would be more severe in young children. However, none of the patients in 2020-2021 actually tested positive for COVID. Increased use of high flow, albuterol, chest radiographs and ICU admissions for bronchiolitis were seen during the lower volume period when rhinovirus was the dominant pathogen detected. Other studies have shown that providers are more likely to utilize diagnostic tests and medications once high flow is initiated, and increased use of low value care for bronchiolitis during lower census periods has been described [18, 19]. Prior studies have not shown an increase in bronchiolitis severity during this time [20]. In 2021-2022, 31% of patients tested had COVID, a substantial increase likely reflecting increased lower respiratory symptoms with changing variants, but albuterol and decreased. The resurgence of bronchiolitis after such a dramatic decrease means this disease is likely never going to completely disappear. Ironically, concentrating quality improvement efforts into periods of low census for a disease may have more impact.
This hospital saw a stark change in the virology of patients seen in the ED with bronchiolitis over the course of the study period. There was an initial disappearance of RSV in the first year of the pandemic with only four RSV cases identified in 2020 among our study population. An atypical summer spike in RSV in 2021 followed, which is likely the primary driver in the increased bronchiolitis visits. The summer ED visits were almost as high as the winter of the last typical season in 2019. During the low volume year of 2020, rhino/enterovirus was the predominant virus detected by percentage, though the raw number detected was relatively similar to previous years. It is possible that more rhinovirus was detected due to higher testing rates, which increased by 23% from the year prior. Rhinovirus is often found to be a co-infection with a large number of asymptomatic carriers but is also known to cause bronchiolitis, especially associated with wheezing, and may be an early predictor of asthma [21-24]. It is possible that more albuterol was used during this time due to more rhino/enterovirus induced wheezing heard on exam.
The dominance of rhino/enterovirus during the emergence of the pandemic and the disappearance of RSV raises important questions about how the transmission of this virus was affected by efforts to slow the spread of COVID. RSV is an enveloped, single‐stranded, negative‐sense RNA virus of the Pneumoviridae family and is transmitted via droplet [24]. Because of its enveloped structure, RSV is more affected by hand washing then the non-enveloped structure of rhinovirus, which has a moderate resistance to hand sanitizer [24, 25]. RSV’s main reservoir is in chronic obstructive pulmonary disease and immunocompromised hosts, whereas rhinovirus is often carried and spread by asymptomatic healthy children [1, 25]. Hand washing was heavily stressed as a non-pharmaceutical intervention during the pandemic and could have decreased RSV transmission but would not have the same impact on rhinovirus. The relative resilience of rhinovirus during the pandemic likens it to the cockroach of viruses- one that never completely disappears and survives most extinguishing efforts.
Immunity to RSV is complex. For infants, the transfer of maternal antibodies can help protect them in the first couple months of life [27]. Adults also need continued antigenic exposure, as it has been shown there is a loss of RSV-specific IgA memory B-cells, usually in the summer months when RSV is dormant [27]. It is reasonable to hypothesize there was decreased maternal antibody transfer to infants by mothers who were pregnant during the early COVID pandemic and were not being exposed to RSV antigens. Therefore it is not surprising there was a large, atypical RSV spike in the summer of 2021 (Figure 2) when there was likely a large population of infants and toddlers who were immunologically naïve to RSV being exposed for the first time. As COVID precautions relaxed in the spring of 2021, RSV was able to have a strong resurgence. The rise in bronchiolitis visits in the summer of 2021 also followed the end of the state mask mandate in this state, which expired in April of 2021. In the future, we will see if this shift in RSV seasonality persists with bronchiolitis becoming a relatively steady year-round illness, or return to previous seasonal norms. This could influence the timing of Synagis given to eligible infants, as it is currently only available during the winter months. It also remains to be seen if other Sars-CoV-2 variants will cause more respiratory illness in this population, as is suggested by the upwards trend in 2021-2022.
This study is limited by being a single-institution, retrospective study. The diagnosis of bronchiolitis was based on ICD-10 coding only and testing from other sources prior to admission were not included. The increased ICU admission rate for bronchiolitis is difficult to interpret as ICU admission criteria changed such that all patients on high flow nasal cannula were admitted to the ICU instead of the step-down unit until their COVID test resulted until November 2020, though the numbers were very small. During 2021 this hospital participated in a Value in Inpatient Pediatrics high flow initiation reduction quality improvement project (HIFLO), which may account for some of the decreased high flow rate from 2020 to 2021. Internal quality improvement projects targeted albuterol use which likely accounts for the sharp decrease from 2017 to 2018.
In summary, COVID-19 had a significant impact on bronchiolitis emergency department visits in overall number, admission rates, an increase in low value care, and virology, while not being the predominant driver of respiratory disease in young children.
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