Researchers from the University of Florida in the USA, and the Centre for Disease Control and Prevention in China analysed the data of 349 people with Covid-19 and 1 964 of their close contacts (household members and family members not living at the same address) in Guangzhou, China.  

Incubation is the danger period  

The modelling research, published in The Lancet Infectious Diseases journal, suggests the coronavirus (SARS-CoV-2) that causes Covid-19 may spread more easily among people living together during the incubation period, which is between 1-14 days. Researchers say the risk of infection is potentially higher during this stage than during the illness period. After one day of exposure, family members were 39% less likely to become infected after symptoms emerged than during the incubation period, while those living together had 41% lower odds.  

“Our analyses suggest that the infectiousness of individuals with Covid-19 before they have symptoms is high and could substantially increase the difficulty of curbing the ongoing pandemic,” says Dr Yang Yang from the University of Florida who co-led the research. 

The analyses estimates that the likelihood of secondary transmission – spread from an infected person to non-household contacts – was 2.4%. The likelihood of passing on the virus was higher among people living together, with an attack rate of 17.1% (or around 1 in 6), and 12.4% (about 1 in 8) among close contacts not living at the same address.  

The model also suggests that the likelihood of household infection is highest among adults aged 60 or older (attack rate of 28% for those living together, and 18.4% for close contacts) and lowest in those aged 20 years or younger (attack rate 6.4% for those living together, and 5.2% for close contacts).   

What it means for us 

The risk to older adults is particularly relevant for South AfricaData from the Gauteng City-Region Observatory (GCRO)a research institute, reveals that in Gauteng 74% of people over 60 live in households of two or more people. Just 16% live only with their spouse. Their households are likely to contain several generations: 59% of the elderly live with family members other than their spouse, and 42% live in households with children under 18 years.  



Professor Salim Abdool Karim, chairman of the Covid-19 Ministerial Advisory Committee previously advised it would be necessary for older household members to self-isolate. But it can be difficult for many elderly people to stay a room of their own without contact with household members if they reside in an overcrowded home. As lockdown restrictions ease and the economy reopensit’s expected that there will be a rise in infections.  

It’s not just immediate household members at risk. In the Western Cape, which is the epicentre of the Covid-19 outbreak in South Africa, hotspot areas like Khayelitsha, Langa and Philippi have to contend with neighbouring homes in extremely close proximity, often closer than the recommended 1.5 metre social distancing measure.  

Speaking to the news website, New Frame, Suhair Solomon, part of the Western Cape Department of Health team coordinating case and contact management, community screening and testing, related one case where a Covid positive individual lived in a two-bedroom house with nine other people. A further eight people were backyard dwellers. Although none displayed any symptoms, Solomon and her team tested them all and 10 of the 18 were Covid-19 positive.  


“Active case finding and isolation in conjunction with comprehensive contact tracing and quarantine will be key to preventing infected contacts from spreading the virus during their incubation periods, which will be crucial when easing lockdown restrictions on movement and mixing,” says Yang.  

But here too, South Africa is on the back foot. The mass testing strategy has failed due to a major backlog in test resultsmaking contact tracing meaningless. Previously, Professor Shabir Moosa from Chiawelo, a community oriented primary health care facility, told Health-e News“The results now take 14-21 days, making them pointless especially for contact tracing unless patients have complied with isolation instructions as if they were positive,” pointing out that not many are self-isolating or are able to do so.    

Dr Tracey Naledi, deputy dean of health sciences at the University of Cape Town holds the same view. In a statement to Health-e News, she says, “In the Western Cape where the burden is highest, the transmission is now mainly in high density, low resourced areas where even self-isolation is challenging, thus it’s difficult to stop the transmission.”   

Naledi adds that “community transmission means that it is not easy to identify the original source of the exposure, and with multiple clusters of infections, contact tracing and quarantine is really challenging”.  

So if household members don’t know that one member may potentially be infectious, how can they protect themselves? It’s important to frequently disinfect commonly shared surfaces, and to open windows and doors for ventilation. The World Health Organisation has indicated asymptomatic (will not develop any symptoms) or presymptomatic people can spread the virus even if they are not coughing through singing, yelling, or even talking, so 
wear masks indoors when in close proximity.  Health-e News  


For more information on Covid-19 in South Africa, you can call the toll-free line on 0800 029 999, or you can send a message that says “Hi” on WhatsApp to the number 060 012 3456. You can also visit the  SA Coronavirus website.