A woman living in a high-rise apartment in the Lal Bahadur Shastri Nagar area of Bengaluru developed fever, headache and body pain last week. She has been homebound for most of the second wave of Covid-19 pandemic. She had not stepped out for the last 10-12 days. The fever came soon after Cyclone Tauktae battered coastal areas of Karnataka and swung weather in Bengaluru.
Among many questions to ascertain the probable reasons of her illness, she wanted to know whether vertical transmission — spread of infection from one floor to other — of Covid-19 was possible. A family above her floor had Covid-19 positive patient(s).
This question has been a subject of interest for researchers since the days of the SARS outbreak in 2002. This study found that SARS transmission between flats on different floors was “a fact”.
The study said, “One of the concerns is that there may be multiple transmission routes across households in high-rise residential buildings, one of which is the natural ventilative airflow through open windows between flats, caused by buoyancy effects.”
“Our early on-site measurement using tracer gases confirmed qualitatively and quantitatively that the re-entry of the exhaust-polluted air from the window of the lower floor into the adjacent upper floor is a fact.”
A study published in December 2020 in the context of SARS-CoV-2 -- the virus behind the Covid-19 pandemic -- found results “consistent with the vertical spread of virus-laden aerosols” between “aligned flats connected by drainage pipes in the master bathrooms”.
This study was conducted to ascertain Covid-19 sources in three families living in China. They contracted Covid-19 between January 26 and February 13 last year.
One of the families had returned from Wuhan, the epicentre of coronavirus outbreak from where it spread to rest of the world. The researchers established that there was no contact between the three families that could have led to transmission of SARS-CoV-2.
The researchers examined the elevator route of transmission and said, “No evidence was found for transmission via the elevator or elsewhere.”
“The families lived in 3 vertically aligned flats connected by drainage pipes in the master bathrooms. Both the observed infections and the locations of positive environmental samples are consistent with the vertical spread of virus-laden aerosols via these stacks and vents,” they said.
This paper examining scientific literature on the possibility of Covid-19 outbreak in high-rise buildings authenticates the probability of the vertical transmission of SARS-CoV-2.
It lists out faulty ventilation systems, air leakage or unintentional air flows and faulty plumbing stacks as the possible means of the spread of Covid-19 in multi-unit residential buildings. This paper lays great emphasis on ventilation systems.
However, some other studies include those conducted in the famous example of a Chinese restaurant where nine people got infected with SARS-CoV-2 in January 2020. The air conditioner was blamed for the infectious spread. But in the same example 79 other diners did not catch the infection.
This indicates that while faulty plumbing, staircases and elevators can be a transmission route of SARS-CoV-2, the HVAC (heating, ventilation, and air conditioning) systems have not been found to be a Covid-19 spreader between flats in high-buildings.
To answer the original question on the basis of studies conducted since the coronavirus outbreak, yes, vertical transmission of Covid-19 from one flat to another in a high-rise building is possible.
Though exact the reasons for such SARS-CoV-2 infection pattern are not clearly established the Brihanmumbai Municipal Corporation (BMC) in March said 90 per cent of all Covid-19 cases in the previous two months came from high-rise buildings in Mumbai.