key: cord-0746990-75xdnevi
authors: Wang, Chao; Yang, Yan‐Na; Xi, Lu; Yang, Li‐Li; Du, Juan; Zhang, Zhong‐Song; Lian, Xin‐Yao; Cui, Yan; Li, Hong‐Jun; Zhang, Wan‐Xue; Liu, Bei; Cui, Fuqiang; Lu, Qing‐Bin
title: Dynamics of influenza‐like illness under urbanization procedure and COVID‐19 pandemic in the subcenter of Beijing during 2013–2021
date: 2022-04-28
journal: J Med Virol
DOI: 10.1002/jmv.27803
sha: b159bd86de16d2f8e549a5ef748d101849654642
doc_id: 746990
cord_uid: 75xdnevi

Influenza‐like illness (ILI) varies in intensity year by year, generally keeping a stable pattern except for great changes of its epidemic pattern. Of the most impacting factors, urbanization has been suggested as shaping the intensity of influenza epidemics. Besides, growing evidence indicates the nonpharmaceutical interventions (NPIs) to severe acute respiratory syndrome coronavirus 2 offer great advantages in controlling infectious diseases. The present study aimed to evaluate the impact of urbanization and NPIs on the dynamic of ILI in Tongzhou, Beijing, during January 2013 to March 2021. ILI epidemiological surveillance data in Tongzhou district were obtained from Beijing Influenza Surveillance Network and separated into three periods of urbanization and four intervals of coronavirus disease 2019 pandemic. Standardized average incidence rates of ILI in each separate stages were calculated and compared by using Wilson method and time series model of seasonal ARIMA. Influenza seasonal outbreaks showed similar epidemic size and intensity before urbanization during 2013–2016. Increased ILI activity was found during the process of Tongzhou's urbanization during 2017–2019, with the rate difference of 2.48 (95% confidence interva [CI]: 2.44, 2.52) and the rate ratio of 1.75 (95% CI: 1.74, 1.76) of ILI incidence between preurbanization and urbanization periods. ILI activity abruptly decreased from the beginning of 2020 and kept at the bottom level almost in every epidemic interval. The top decrease in ILI activity by NPIs was shown in 5–14 years group in 2020–2021 influenza season, as 92.2% (95% CI: 78.3%, 95.2%). The results indicated that both urbanization and NPIs interrupted the epidemic pattern of ILI. We should pay more attention to public health when facing increasing population density, human contact, population mobility, and migration in the process of urbanization. NPIs and influenza vaccination should be implemented as necessary measures to protect people from common infectious diseases like ILI.

Outbreaks of influenza-like illness (ILI) have led to huge socioeconomical and health burden, of which three to five million cases experience severe illness. Influenza virus is one of the most common pathogen that cause respiratory diseases, such as ILI, particularly in autumn and winter seasons in China. 1 About 290-450 thousand deaths are attributed to seasonal influenza worldwide. 2, 3 Among the most impacted countries, three million ILI cases and over 80 000 ILI-related deaths were estimated annually, even though marvelous efforts have been made to mitigate its impacts, such as etiological detection, routine epidemiological surveillance, or vaccination extension. 4 Increasing concerns have underscored the importance of linkages between the threats of infectious diseases and fastspreading urbanization. 5 In particular, of the most impacting factors, urbanization has been suggested as shaping the intensity of influenza epidemics, due to the increasing population density, human contact, population mobility, migration, and so forth. [6] [7] [8] As a mushrooming subcenter of Beijing, Tongzhou district has been initialing its urbanization, with a boosting population increase from 1.25 million in 2013 to 1.65 million in 2020. 9 Since its urbanization was accelerated from 2017 and came on stream from 2019, 10 local reports have indicated intensified seasonal ILI epidemic and sporadic infections. 11 However, at the initial stage of urbanization of Tongzhou district, the dynamic pattern of ILI in this area remains uninvestigated before, during or after its urbanization procedure, as well as population difference.

One year after the official operation of Tongzhou subcenter at the beginning of 2020, the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has caused ongoing huge damage to human health. 12 Before massive vaccination to SARS-CoV-2 by March 2021, the nonpharmaceutical interventions (NPIs), including social distancing, mask-wearing, shelter-in-place, travel restrictions, school closure, and so forth has been orientated to be the main measurements in preventing the pandemic. 13, 14 Studies have explored the impact of COVID-19 pandemic and related NPIs on respiratory diseases like influenza, since they share similar transmission modes and symptoms. 15, 16 Several studies indicated that the activity of ILI generally decreased by NPIs in the short run. [17] [18] [19] However, the impact of NPIs on ILI dynamic after the first wave was still needed to be illustrated.

In the present study, the local ILI epidemiological surveillance data were extracted from the interval during 2013-2021, with four periods as preurbanization, interim, urbanization, and pandemic era.

Epidemic patterns of ILI within such four periods, as well as the impact of urbanization and NPIs on the dynamic of ILI, were analyzed and compared. The findings will contribute to our understanding of how urbanization influences the epidemiological pattern of local diseases and offer a clue for ILI NPIs' prevention at the initial of urbanization. 20 Demographic data including population size of each age group was collected from Beijing Statistical Yearbook from 2013 to 2020. 9 As influenza vaccine was integrated into the local immunization plan for school aged children and the elders, vaccination data among those aged 5-14 years and ≥60 years was further extracted from public database from Tongzhou CDC, Beijing, to provide insight into the influence of influenza vaccination on the dynamic change of ILI cases in this area.

Individuals with either cough or sore throat with temperature ≥38.0°C

were recorded as ILI cases. We extracted and summarized the ILI cases in BISN from January 2013 to March 2021 for present study. 20 

Weekly incidence rates of ILI were based on the total cases and agespecified population sizes within 1 week and were illustrated within our study interval between January 2013 and March 2021. To demonstrate the impact of urbanization on the epidemic patterns of ILI, population standardized average incidence rates of ILI in the three separate urbanization stages were calculated. The average incidence rates of ILI among three urbanization periods were then compared by using rate difference and rate ratio with Wilson method, as well as their 95% confidence interval (95% CI). 21 

The prepandemic years from 2013 to 2019 were categorized into three periods ( showed the largest rate ratio as 3.07 (95% CI: 3.00, 3.14), and those aged 60 years or above presented stable ILI activity with the rate ratio negative correlation between vaccination coverage and ILI rates as the correlation coefficient of −0.46 and −0.39 among these two age groups, no statistical significance was found due to the limited sample size (Supporting Information: Table S1 ).

Generally, the increased ILI activity was found during the process of on influenza among the youth and adults might be a supplementary measure in protecting the whole population from ILI infection, besides

NPIs or personal protection measures. 37, 38 In contrast to preurbanization period or urbanization period, the activity and spread of influenza virus were considerably interrupted during COVID-19 pandemic period, particularly during influenza epidemic season. Studies have offered similar results in other countries or areas like Canada, 39 America, 40 Southeastern Asia, 41 eastern Asia, 42, 43 Europe, 44 as well as China 15, 16 considering the circulation level of influenza or similar infectious respiratory diseases. The situation is suggested largely attributed to the widespread implementation of NPIs since COVID-19 became a serious concern to population health. 16 Under the stressful health pressure, people also began to acquire more self-protective measures to avoid the infection of COVID-19. 15 

The authors declare no conflicts of interest.

The data that support the findings of this study are available from the corresponding author upon reasonable request. The original data set can be directed to the corresponding authors.

The following information was supplied relating to ethical approvals: The Peking University Institutional Review Board Office granted Ethical approval to carry out the study within its facilities (IRB00001052-19005).

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http://orcid.org/0000-0002-2804-0827