key: cord-0848064-r98k187t
authors: Teng, Jade L L; Fok, Kenny M N; Lin, Ken P K; Chan, Elaine; Ma, Yuanchao; Lau, Susanna K P; Woo, Patrick C Y
title: Substantial decline in invasive pneumococcal disease (IPD) during COVID-19 pandemic in Hong Kong
date: 2021-04-27
journal: Clin Infect Dis
DOI: 10.1093/cid/ciab382
sha: 18df41e5805192728994913cb86ad64999737aa4
doc_id: 848064
cord_uid: r98k187t

Compared to other countries, a more substantial decrease of invasive pneumococcal disease incidence was observed in Hong Kong, which is most likely attributable to the proactive mass adoption of face masks by the public. Human behavioral changes, particularly mask-wearing, should be considered as an additional prevention strategy against IPD.

A c c e p t e d M a n u s c r i p t 3 The COVID-19 pandemic has resulted in dramatic human loss worldwide. The first COVID-19 case was confirmed in Hong Kong on 23 January 2020 and was followed by several waves of the disease. As of 31 December 2020, Hong Kong had recorded 8, 847 confirmed cases, with 26.7% being locally acquired [1] . Overall, Hong Kong has kept a relatively flatter epidemic curve than most other places. This is quite remarkable considering that Hong Kong is an international transport hub, in close proximity to China, and one of the most densely populated areas in the world. The city also did not enter any stage of complete lockdown. Hong Kong is one of the locations affected by the SARS outbreak in 2003 and aggregated a total of 299 deaths, representing the second highest mortalities after China. It is believed that the SARS experience largely influenced the personal behavioral changes of citizens in response to the COVID-19 epidemic. In fact, the psychological impact of the SARS outbreak was so huge that hygiene became second nature and Hong Kong was among the first places to initiate proactive mass adoption of face masks in public areas as personal protection, many months before face masks were made compulsory by the government in July 2020.

Invasive pneumococcal disease (IPD) is caused by Streptococcus pneumoniae and transmitted via respiratory droplets. Carriage of S. pneumoniae is a prerequisite for developing IPD and is commonly found in young children who are considered the source of pneumococcal infections and spread in the community. Since IPD is a leading cause of mortality and morbidity in our locality, it was listed as a statutory notifiable disease in 2015 [2] . Pneumococcal vaccination is one mean of preventing IPD and Hong Kong was among the first Asian cities to include pneumococcal conjugate vaccine in its childhood immunization program in 2009 [2] . The latest recommendation is PCV13 with vaccination rate of 99.5% in children. However, the coverage of vaccination in the 65 years or above remained low with only 45.8% of this high-risk category vaccinated. Before the COVID-19 A c c e p t e d M a n u s c r i p t 4 pandemic, the IPD incidence in Hong Kong was still high. IPD also causes significant burden of illness in Singapore and Taiwan and was listed as a statutory disease in 2010 and 2007 respectively [3, 4] . Recent studies in Singapore and Taiwan have reported reductions in IPD cases during the first few months of the COVID-19 pandemic [5, 6] . In Singapore, a 42.9% decline of IPD cases in an institution was recorded in the first 27 weeks of 2020, while Taiwan recorded a 50.9% nationwide reduction in IPD cases during the first eight months of 2020. We hypothesized that the marked behavioral changes, particularly the proactive mass adoption of face masks, of Hong Kong citizens should have a more prominent effect on reducing IPD cases during the COVID-19 pandemic. To test the hypothesis, we analyzed IPD case numbers in 2020 and compared the monthly and yearly trends to the data in the previous five years in Hong Kong. We also extended the analysis of IPD case numbers in Singapore and Taiwan to the entire 12-month period in 2020 and compared it with trends from the previous five years in the respective places and Hong Kong. Since IPD is a serious disease that can become life-threatening if untreated, individuals would seek prompt medical attention when infected. Therefore, data collected through reportable disease registries truly reflect the actual number of IPD cases in the respective countries.

Seasonal autoregressive integrated moving average models were applied to monthly IPD cases in 2015-2019 inclusively to predict those of 2020. Stepwise model selection based on Akaike Information Criterion were performed (Supplementary Table 1 ). Twelve-step predictions and prediction intervals were generated for each place to forecast the respective monthly cases in 2020. monitored at the main entrances during lunchtime, the busiest hour of the venues. We found that >99% of people wore masks, including children (Supplementary Figure 1a) , consistent to findings reported in previous studies [10] . In addition to mask-wearing, hygiene awareness was raised, including use of hand sanitizers, improved protection for high contact surfaces, temperature checking, social distancing and limiting restaurant dining services and gathering sizes (Supplementary Figure 1) . In May and August, when the number of confirmed local COVID-19 cases were kept low for over three weeks, restrictions such as gathering sizes and various commercial activities were lifted and schools reopened. However, the mask-wearing practice was continued and the number of IPD cases remained low (Figure 1a ). Considering that no changes had been made to the pneumococcal vaccination strategy or the reporting requirements, and there is no change of dominant serotype, it is highly likely that the proactive actions of the public, particularly mask-wearing, in response to the COVID-19 pandemic, contributed to the decline in IPD incidence in 2020. This is further supported by a similar marked decline in IPD cases observed in Singapore. After an initial surge in mask usage in January, the Singapore government advocated their citizens in February to use masks only if unwell. In March, measures were reviewed and masks were made mandatory in April, resulting in a rise of mask-wearers from 23% in March to 90% in April [11] . The response in mask-wearing was reflected in their monthly IPD case numbers, with an average reduction of 39% in January-April, followed by a marked average reduction of 86.4% in May-December (Figure 1b) . This corresponded to the first significant drop in IPD cases observed in June (Figure 1e, Supplementary Table 3 ). Comparatively, Taiwan recorded a relatively smaller reduction of IPD cases compared to Hong Kong and Singapore (Figure 1e ).

Although initial proactive use of masks in Taiwan was rapid, we speculate that due to their early success (zero local COVID-19 case for over eight months in 2020) through strict border controls, mask usage was not as compliant and face masks were not mandatory until 

The Centre for Health Protection of the Department of Health, Hong Kong. The latest situation of cases of COVID-19

Increase in incidence of invasive pneumococcal disease caused by serotype 3 in children eight years after the introduction of the pneumococcal conjugate vaccine in Hong Kong

Role of pneumococcal vaccination in prevention of pneumococcal disease among adults in Singapore

Pneumococcal disease and use of pneumococcal vaccines in Taiwan

Decline in pneumococcal disease incidence in the time of COVID-19 in Singapore

Decline in invasive pneumococcal disease during COVID-19 pandemic in Taiwan

The Centre for Health Protection of the Department of Health, Hong Kong