A new study reports the results of a viral detection study carried out in buses used for public transport across the final week of lockdown, as travel restrictions were being lifted step by step. This study by Italian researchers and published on the preprint server bioRxiv* in June 2020, may help to understand how a virus can spread within a city bus during normal operation and how effective are the measures used to protect against such transmission.
Even as the COVID-19 pandemic continues to spread, with over 10 million cases and 500,000 deaths, the only effective way to counter it has been through non-pharmacological interventions (NPI) such as lockdown of entire regions, physical distancing during essential social interactions, the use of face masks outside one’s home, and to practice diligent hand hygiene.
However, with the first peak of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) outbreak now over in a few regions, lockdowns are being relaxed in various ways and at a different pace, according to each government’s policy. The current study was timed for the last weeks of lockdown when the substantial travel and social gathering restrictions in Italy were being relaxed.
Public Transport Hygiene
At the same time, essential services were being regulated strictly to safeguard workers in these fields as well. Cleaning and disinfection of public transport vehicles, and rules to minimize transmission, were put in place. High-touch surfaces like handles and rails were to be cleaned frequently as an aerosolized virus can remain in the air for up to 3 hours, and viral particles can be detected on cardboard for 24 hours, and on plastic or stainless steel for three days.
SARS-CoV-2 asymptomatic infection is another possible route of spread, and crowding also increases viral transmission. Therefore, in Italy, it was recommended that virucidal products be used to sanitize surfaces inside buses. These were based on either chlorine or alcohol application following detergent-based cleaning.
In the region of Abruzzo, Italy, where the study was carried out, the regulations stipulate that not more than 40% of seats and 15% of standing places may be filled, and these were to be demarcated, along with frequent hand sanitization, rear-door onboarding, and obligatory use of masks.
The bus in the current study was cleaned daily with the above solution. Once a week, it was sanitized using an aerosol of highly oxidizing disinfectant and ozonized for 10 minutes. Each bus shift lasts about 6.5 hours.
The Study: Testing Surface and Air Samples from the Bus
About 1,100 passengers traveled by this bus over the period of observation, from May 12 to 22, 2020, in the Abruzzo town of Chietti. The bus route covered 20 km, with 50 stops. There were about 120 passengers per shift.
Samples were collected each day except on weekends, for one shift of the bus, covering five routes. The surface samples were collected from five high touch points before and after each bus shift, as reference and study samples, respectively. Air samples were collected over the daily shifts. Microbiologic gelatin filters were also used for airborne virus detection, one near the ticket machine and one near the rear door.
They were tested by real-time reverse transcriptase-polymerase chain reaction (RT-PCR) for the SARS-CoV-2. Since none of the passengers were tested, the number of infected individuals on the bus during the observation period is not known. However, the proportion of asymptomatic people in the population is about 40% to 45%, by current estimates.
Thus, if about 30% of people who traveled on the bus were infected and asymptomatic, this would mean that each journey had about 37 such travelers who could have touched the surfaces sampled.
Implications for Viral Control in Public Transport
All surface and air samples proved negative for viral genes. If this is true, this means that the current cleaning and sanitization requirements – alcohol-based sanitizer use at the door of entrance, and wearing gloves - are adequate to keep the surfaces and air inside the bus virus-free.
Meanwhile, the use of a facial mask and keeping the windows open during the ride allows free ventilation and prevents the virus from spreading to other passengers through the air. This finding also agrees with earlier studies that show facial masks prevent viral spread by aerosols and droplets emitted by asymptomatic people, as does free ventilation of confined spaces such as within a city bus.
The end of a lockdown imposed to combat a viral pandemic is always a tension-fraught period, as growing numbers of individuals re-enter the travel mainstream, among other activities. The current study shows that public buses can be safely used to convey passengers even in the presence of about 30% asymptomatic but infected individuals if safety requirements are observed.
These measures include hand sanitization, cleaning and disinfection of surfaces, and prevention of air transmission by excellent ventilation, coupled with personal precautions such as the use of facial masks and social distancing.
The researchers sum up: “Our findings confirm that the measures established for public transport in terms of sanitation, air ventilation, and interpersonal precautions are effective, at least during this study, to make healthy and COVID-free the environment inside the buses.”
bioRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.