COVID-19 – transmission and clinical characteristics

The first cases of COVID-19 before January 2020 were linked to the Huanan Seafood Wholesale Market and zoonotic (animal-to-human) transmission was believed to be the main mechanism. The emergence of the virus coincided with the Chinese Lunar New Year Holiday, in which a large human migration of 5 million people took place as city workers travelled back to their hometowns. From the currently available data available to this date, the main mode of human-to-human transmission occurs through close contact with an infected individual and exposed to droplets or aerosols. When the infected individual is coughing or sneezing, these aerosols are believed to enter the lungs via inhalation through the mouth or nose.³ The virus was detectable in stool samples despite the course of illness, even after the virus was no longer detected in respiratory samples.⁸ The contaminated environment may cause transmission through contact with mucosal membranes, such as the eyes, mouth, and nose.⁹ Studies have also shown that the virus is viable up to hours as aerosols and days on surfaces.¹⁰

The average median incubation period was estimated to be around 5 days, majority of those who will develop symptoms will do so within 11.5 days, and approximately 1% will develop symptoms after 14 days.¹¹ The estimated R₀ was approximately 2.2, which means that on average an infected person will transmit the virus to approximately 2 other individuals.¹²

The most common symptoms were fever (43.8% on admission and 88.7% during hospitalization) and cough (67.8%).¹³ Infected people were often asymptomatic and did not present with a fever, which will impose a challenging situation in terms of developing a surveillance method for sporting events. The viral load detected in symptomatic and asymptomatic patients were of similar levels and the viral nucleic acid shedding pattern of infected individuals was more similar to influenza rather than SARS in 2003, implying that asymptomatic infected individuals are as infectious as those that are showing symptoms.¹⁴ This further differentiates why SARS was an epidemic and COVID-19 is a pandemic, suggesting that infection control measures and protocols developed for SARS may not apply to the current COVID-19 pandemic.

Preventive measures

WHO recommends countries to actively combat the disease through critical preparedness, readiness, and response actions according to the “Strategic Preparedness and Response Plan for COVID-19” and their corresponding “WHO defined transmission scenario”.¹⁵

Recommendations include measures to control local spread by raising public awareness, promotion of personal hygiene, and postponement or cancellation of large-scale public gatherings. In the situation of identifying positive cases, they should implement case and contact finding through containment to delay surges of infected individuals.¹⁶ Sporting events could be considered a large-scale public event, whether-or-not a spectating crowd is present. If sporting competitions are to be resumed, the goal is to minimize the number of people congregated at one single place and time through closed competitions with no spectators and minimizing nonessential personnel present at the venue, such as by cancelling press conferences and interviews.

Sporting equipment should be cleaned as frequently as possible as SARS-CoV 2 was found to last longer on surfaces such as plastic and stainless steel up to 72 h. A dilution of 1:50 of standard bleach for large settings and 70% ethanol is recommended for smaller surfaces.¹⁷

Immunity and sports

Although moderate-levels of exercise can boost overall immunity.18, 19, 20, 21 Intensive and prolonged physical exertion has been linked with an ‘open-window’ of impaired immunity up to 72 h after the exercise.22, 23, 24 Common infections for athletes mostly comprises of dermatological related infections (especially in contact sports),²⁵ upper respiratory tract infections, and gastrointestinal infections. The coronavirus is a respiratory pathogen and previous studies have shown that the risk of upper respiratory tract infections was almost six times more likely in endurance races.^19,26,27 The underlying mechanism is not fully understood, although most studies suggest exercise significantly influences acquired immunity while evidence about the role of exercise on innate immunity is less conclusive. As the virus was also found in stool samples,⁸ contaminated environments, such as soil, may pose a threat to outdoor sporting events. There are still unknowns regarding the relationship of immunity and sports, therefore experts are still researching on the role of psychological factors (especially during competitions) as one of the large knowledge gaps.²¹

Regarding the topic of infection control during a global pandemic, our focus is not whether these infections hamper athletic performance; but lies in the assessment of the risk of a player getting infected if they participate in sports and measure on how to reduce the rate/risk of transmission. Our experience in the local top-tier league will illustrate the measures that were taken and the rationale behind them.

Experience in the professional football league

Hong Kong Premier League (HKPL) is the top-division professional football league in Hong Kong with 10 teams competing. Unlike other Asian football leagues which start their season in February or March, HKPL starts in August or September. This made HKPL the first professional football league in the world to be suspended on January 28, 2020²⁸, as a result of COVID-19 outbreak in Asia.

Two weeks later, although the official government policy was still unclear, the Hong Kong Football Association (HKFA) decided to resume its annual cup competition.²⁹ Sixteen cup matches were held behind closed doors in the HKFA training centre from February 11–29.

With the support from the Hong Kong Government, HKPL regular league matches were resumed on March 7 behind closed doors in Tseung Kwan O Sports Ground (TKOSG), which is a certified stadium for professional football matches.³⁰ There were a number of new measures for protection against COVID-19 transmission. Firstly, the number of personnel in the stadium was limited to 180. All personnel were required to submit health declaration forms on arrival, followed by measuring body temperature and using sanitizing alcohol. Meeting rooms were arranged for teams to have pre-game, half-time, and post-game briefings instead of in the changing room. A maximum of 9 players was allowed to use the changing room at the same time to decrease the chance of close contact and players were not allowed to shower after games as shower water and aerosolized shower mist are a potential medium of infection.³¹ Furthermore, all players and staffs had to wear a surgical mask if not playing And pre-game handshaking were discouraged.

With these strict infection control measures, 10 league and cup matches were held till March 23, in which HKFA decided to stop the competition again due to a rapid surge of imported COVID-19 cases in Hong Kong.³² Unfortunately, a staff of the HKPL team had been confirmed to have COVID-19 infection on March 31, after his spouse was confirmed to be infected on March 29.³³ There has not been anymore reported cases in the HKPL till the date of this writing. The timeline and trend of HKPL during the COVID-19 outbreak in Hong Kong can be seen in Table 1 and Fig. 1.³⁴

Table 1. Timeline of the HKPL with confirmed cases in Hong Kong.

Timeline	Major event in HKPL	Number of confirmed COVID-19 cases in Hong Kong
January 1, 2020	HKFA Suspend all competition FTC open for team training	8
February 2, 2020	HKFA re-open competition at FTC FTC open for team training	24
March 3, 2020	HKFA Continue competition at TKOSG FTC open for team training	100
March 23, 2020	HKFA Suspend all competition FTC closed	351
March 31, 2020	First confirmed COVID-19 case	680

1. Download : Download high-res image (400KB)
2. Download : Download full-size image

Fig. 1. Status of the HKPL during the COVID-19 outbreak in Hong Kong.

The risk of virus transmission during football games

Avoiding contact and good personal hygiene are key to prevent infection transmission. However, bodily contact is inevitable in football training and competitions. In addition, infection-risky behaviours, such as spitting and touching the face, are not uncommon during football games.

The mean close-contact time for each footballer was 19.3 min per 90 min (Range 5.9–35.5). Although this may seem less than other close-contact sports such as those with smaller courts or close combat sports, infection-risky behaviours were indeed observed in football players. There was an average of 52 episodes of infection-risky behaviours per 90 min of professional football. This reaffirms that playing football certainly poses an infection transmission risk.

Investigation on the effects of exercising with a facemask

In order to maintain physical activity during the COVID-19 control period, many families avoided the crowded city centres and opted to travel to the countryside for a leisurely walk or hike during the weekends. This issue of wearing facemasks during outdoor activities became a topic of interest. The objective of this experiment was to investigate the effects of a facemask during exercise.

This was a controlled laboratory, within-subject, repeated measures study of 23 healthy volunteers of various sporting backgrounds. The participants underwent graded treadmill (10% slope) walking at 4 km per hour for 6 min with the intention of simulating outdoor recreational hiking on an uphill slope at a comfortable pace.³⁵ Heart rate (HR) was continuously monitored using a chest strap (Polar H10) and rate of perceived exertion was charted minute by minute. The rate of perceived exertion (RPE) rating is based on a 6 to 20 rating scale which was measured at rest and also the end of each minute interval with a total of 6 min. All participants repeated the test with and without wearing a surgical mask (in a randomized order); sufficient rest was given between trials. Informed consent was obtained from all participants prior to the testing.

Based on this pilot data, we believe that exercising with facemasks at a submaximal level induces higher physiological responses possibly due to restricted ventilation, heavier breathing, and sympathetic responses.^36,37 Comparing with subjects who did not wear masks (RPE = 10.8 vs 12.7 at 6th min), subjects wearing masks reported subjectively higher physiological demands. A RPE = 12.7 refers to moderate-intensity activity according to the Borg Scale level of “somewhat hard”. Some volunteers reported having an uncomfortable feeling of dyspnoea during the assessment with facemasks on, which was in line with previous studies.³⁸ Skin irritation and accumulation of moisture inside the masks also negatively impacts respiratory and dermal mechanisms of human thermoregulation through impairment of convection, evaporation, and radiation processes.

With the increased cardio-respiratory burden following masked exercise, it is important to stay within safe limits. This is especially true for more mature hikers and those with multiple comorbidities; in general, it will be wise to rest when the heart rate exceeds 150 beats per minute³⁹ and/or 70% of age-predicted maximum heart rate. Masked exercises increase physiological demands, therefore activities should be adjusted according to the individual’s ability.

Elite sports training in Hong Kong

As the only elite training centre in Hong Kong, the Hong Kong Sports Institute (HKSI) has implemented policies in accordance with the pre-determined guidelines related to infection outbreak since early January 2020. These policies emphasize the importance of personal hygiene, the establishment of a reporting system and the prevention of the COVID-19 risk to HKSI to maintain the elite training especially for the Olympic Games/Paralympic Games athletes. From the lesson of the 2003 SARS epidemic in HK, HKSI has well-studied related preventive measures⁴⁰ and drafted corresponding guidelines against different levels of an outbreak which were working alone with updating guidelines from the Department of Health, HKSAR.

Since the launch of the “Preparedness and Response Plan for Novel Infectious Disease of Public Health Significance” and activation of the “Serious Response Level” by HKSAR Government on January 4, HKSI has followed the pre-determined guidelines to clarify the details of precaution measures. Therefore, HKSI was able to take swift measures to respond to the current epidemic situation within a few days. In addition, HKSI issued weekly updates to remind all personnel on personal and maintaining physical distance between individuals during and after training. Relevant health education and psychology supporting materials were provided to strengthen the importance of personal hygiene in HKSI premises and manage pressures that may be encountered when athletes train and compete overseas, respectively. Concomitantly, the cleaning and disinfection of facilities were further enhanced.

As the gravity of the COVID-19 outbreak unfolded with confirmed human-to-human outbreaks in Hong Kong, HKSI escalated the response level to “Emergency” and “Urgent” on January 25 and March 18, respectively. All personnel were required to measure body temperature and declare FTOCC (Fever, Travel, Occupation, Contact and Clustering) status before entering the institute and the daily body temperature report of all athletes were obtained. Upon the issuance of Government “Red Outbound Travel Alert”, all personnel returning to Hong Kong after March 5 from overseas must report their temperature and symptoms (if any) electronically for 14 days and optional COVID-19 tests were provided.

All junior-level and part-time training were suspended and only full-time and Olympic Games/Paralympic Games training continued starting on January 28. A work-from-home roster and flexible office hours have also been implemented for administrative staff, and they were instructed not to have direct contact with athletes. The HKSI strictly abided-by the government’s policy on inbound travellers, all activities to Mainland China and mass activities in HKSI were suspended from February 8 onward. All personnel returning from COVID-19 affected areas (even if not included the governments’ compulsory quarantine regions) were required to self-isolate at home or a hotel for 14 days before returning to HKSI. All travel to the affected areas were disallowed during the corresponding period. On March 25, 80 athletes (Olympic Games/Paralympic Games), 30 coaches, and 20 supporting staffs were present at HKSI to maintain training and related operations at the institute during this lockdown environment. The institute strives to support elite training while preventing an outbreak through proper planning and timely implementation of multiple policies.

As the number of confirmed cases in Hong Kong plateaued and no locally acquired cases were reported from April 21 for 17 days, all full-time senior and junior athletes along with part-time athletes of only Olympic Games and Paralympic Games squads of HKSI gradually resumed their training on May 8 with strict infection control measures as mentioned above. Local schools were allowed to open by phases from May 27, therefore all other junior and part-time athletes were allowed to resume their training and HKSI was completely reverted back to normal training.