#17,957
Long before COVID began its world tour in early 2020, researchers have been examining the risks of using public transportation (buses, trains, aircraft) during infectious disease outbreaks (see 2010's BMJ: Flu Transmission Risks On Airplanes).
Admittedly, between past studies, anecdotal reports, and common sense it is pretty well accepted that the more people you cram into a confined space (bus, train, plane, cruise ship, office, classroom, etc.), the greater the chances of influenza/COVID transmission.
However, by studying the transmission of infectious diseases in these environments, we can devise ways to mitigate the risks (see Study: Simulated Influenza A Transmission In An Office Environment).
In 2008, in Japan: Social Distancing Test On Commuter Trains, the Transport Ministry's Research Institute conducted tests to determine the number of passengers a railway car could safely carry following the outbreak of a new influenza strain in that country.
Their estimate? Only 20% of normal capacity.
In 2011's Viruses With A Ticket To Ride, a study in BMC Infectious Diseases looked at the incidence of ARI (Acute Respiratory Infection) presenting within 5 days of train or tram travel in the UK.
They found that recent bus or tram use was associated with an almost six-fold increased risk of consulting for ARI.
More recently, in 2018's J. Envir. Health: Link Between Public Transport Use & Airborne Transmission Of Infectious Disease, we saw a study that - using some pretty heavy statistical analyses that are well above my pay grade - suggested a link between travel on the London Underground and the spread of respiratory infections.
The rapid spread of COVID among travelers was well demonstrated during the opening days of the 2020 emergency when hundreds of people aboard multiple cruise ships were infected (see Japan MOH: 3rd COVID-19 Death From Diamond Princess - 57 New Positive Cases).
All of which brings us to a new study - published this week in the EID journal - that attempts to further quantify the risks of travel by bus during an outbreak, including `short-term' exposures which have previously been regarded as posing a `lower risk' (see CDC Revises Definition Of `Close Contact' With A COVID Case).
Due to its length, I've only posted some excerpts. Follow the link to read the full report. I'll have a postscript after the break.
Bus Riding as Amplification Mechanism for SARS-CoV-2 Transmission, Germany, 2021
Meike Schöll2, Christoph Höhn2, Johannes Boucsein, Felix Moek, Jasper Plath, Maria an der Heiden, Matthew Huska, Stefan Kröger, Sofia Paraskevopoulou, Claudia Siffczyk, Udo Buchholz3, and Raskit Lachmann3
Abstract
To examine the risk associated with bus riding and identify transmission chains, we investigated a COVID-19 outbreak in Germany in 2021 that involved index case-patients among bus-riding students.
We used routine surveillance data, performed laboratory analyses, interviewed case-patients, and conducted a cohort study. We identified 191 case-patients, 65 (34%) of whom were elementary schoolchildren. A phylogenetically unique strain and epidemiologic analyses provided a link between air travelers and cases among bus company staff, schoolchildren, other bus passengers, and their respective household members.
The attack rate among bus-riding children at 1 school was ≈4 times higher than among children not taking a bus to that school. The outbreak exemplifies how an airborne agent may be transmitted effectively through (multiple) short (<20 minutes) public transport journeys and may rapidly affect many persons.
Several waves of COVID-19 have occurred in Germany (1). After low incidence rates in summer 2021, case numbers started to increase in late August because of the Delta variant (2). During the fourth COVID-19 wave in mid-September 2021 (1), a local public health authority (PHA) noticed an unusual increase in SARS-CoV-2 infections involving local schools in and around a city within the state of Hesse. The 7-day incidence of SARS-CoV-2 infection in this district reached 103 on September 15, compared with 99 in Hesse and 84 nationwide (Robert Koch Institute database, unpub. data).
(SNIP)
On September 30, 2021, local and state PHAs invited the Robert Koch Institute (RKI), Germany’s national public health institute, to jointly investigate the outbreak with the following 3 objectives: to describe the outbreak, its emergence and control; to identify potential sources and chains of transmission through a combination of epidemiologic investigations and whole-genome sequencing (WGS); and to investigate the risk, preventive factors, and modes of transmission, in particular with regard to the role of bus riding. We subsequently explored the role of bus transportation for SARS-CoV-2 transmission and the value of genomic data as a tool for identifying transmission chains.
(SNIP)
Discussion
Using integrated epidemiologic and genomic data, we documented the introduction of a novel SARS-CoV-2 strain (AY.103) to Germany by air travelers, leading to an outbreak. Our investigation also highlights effective transmission of the SARS-CoV-2 Delta variant on a bus.
Most likely, at the time of arrival in Germany, the virus spread from the air travelers to the bus driver, who during the following days may have transmitted the virus to the bus-riding schoolchildren and other passengers.
The outbreak spread further within the bus company, schools, and corresponding households. To our knowledge, further transmission was prevented because of measures such as testing and quarantine implemented by the PHA after outbreak detection.
(SNIP)
Our report showcases how local bus transportation amplified a COVID-19 outbreak. In collaboration with the affected local institutions and bus company, the local PHA rapidly identified the ongoing COVID-19 outbreak and implemented successful measures to control it. Regular testing at school enhanced early detection of SARS-CoV-2 infections, and early quarantine helped minimize subsequent transmissions at school and shows the value of quarantine measures for nonvaccinated contact persons at that time. WGS was essential for proving transmission chains.
To identify and resolve respiratory virus superspreading events, use of public transport and multiple short (<20 minutes) bus rides should be considered as potential amplification mechanisms. PHA should also consider WGS as a useful early adjunct tool for outbreak investigations. Hygiene measures, such as regular testing and mask wearing, should be implemented indoors and also during transportation during similar epidemics or pandemics.
Dr. Schöll is a medical doctor and political scientist. She works as an epidemiologist; her research interests are infectious disease epidemiology, crisis management, and evaluation.
While the mandate to wear masks while on public transport was still in effect in Germany at the time of this outbreak - after nearly 18 months compliance had decreased - as described in the following passage:
Bus Driver and Bus Properties
The school bus driver tested positive for SARS-CoV-2 on September 15. As a close contact of a SARS-CoV-2–infected person and lacking vaccination, starting September 13, he was required to be quarantined.
We were told that he instead drove the public bus, the school bus, and 1 charter tour bus (with female day-trippers) until September 15. In addition, several bus passengers (or their parents) reported that the bus driver was coughing and not wearing a mask for several days until he tested positive on September 15.
The obligation to wear masks during the ride was not generally enforced on the bus. The bus provided fresh air through air conditioning and regular air circulation; the 2 roof openings were not regularly opened in September.
In the opening weeks of COVID - in places like Japan, South Korea, and Thailand - many of the first cases identified were among tour guides and/or taxi/bus drivers (see here, here, here, here, here, and here).
Today's study illustrates how quickly a superspreading event can occur when a public transport driver is infected, and worse, doesn't follow the rules.
Luckily, COVID was a relatively mild illness in school-aged children. We may not be so lucky next time. Which is why it is important to take the lessons of the past 4 years seriously.
