Mild to moderate cases in home isolation can infect only one-third contacts: WHO-MAMC study

Mild to moderate coronavirus cases under home isolation can infect only one-third of contacts in seven to 10 days of exposure and thus there is no need to set up special Covid care centers for such patients, according to a study conducted over six months in Delhi.

Maulana Azad Medical College, which conducted the research with the support from the World Health Organization and the Delhi government included 109 households from Central and Northeast districts in the study conducted between December 28, 2020, and June 28.

”The secondary attack rate (SAR) estimated was 13.86 percent and the secondary infection rate was 33.16 percent. The proportion of secondary cases being symptomatic and asymptomatic was 34.78 percent and 65.22 percent, respectively,” the report titled.

”A prospective study on the transmission dynamics of coronavirus disease-2019 (Covid) among household contacts in Delhi” read.

The study led by Dr Pragya Sharma, Professor, Department of Community, MAMC, suggested that not all the individuals in contact with the primary case will get the disease. The transmission will depend upon the viral excretion in the primary case. Also, factors like sharing utensils can increase the risk of the infection. Thus, despite similar factors in the household contacts, only one-third contacts will get the infection in 7-10 days of exposure, it said.

”Therefore, there is no need to set up special COVID care centers for patients having mild to moderate disease and can be taken care of in their homes,” the study said.

The research also showed that hospitalisation rate in the patients suffering from mild or moderate disease was very low (1.1 percent) and that too with comorbidity. Obesity was the only factor seen to be associated with the worsening of the disease. ”Thus, the role of primary healthcare workers in regular monitoring of the patients in mild or moderate category with obesity and timely referral should remain priority. The hospitals should also keep a buffer of services for these 1.1 per cent patients on home care that might require hospitalisation in due course of disease; which could translate into huge numbers in the time of pandemic,” it said. The investigators said the finding of a secondary infection rate of 33 per cent also suggests laxity in following Covid-appropriate behaviour. Therefore, it is needed that the primary case and their contacts need to maintain COVID-19 appropriate behaviour at all times. The primary case under home isolation and their household contacts need to strictly adhere to the home isolation guidelines of not sharing a common room, toilet, utensils and following infection prevention protocols, they said.

Dr Sharma said 89 per cent of the primary cases had developed antibodies by the 28th day of contact, whereas the rest remained seronegative. ”This implies that almost one out of 10 primary cases may never develop the antibodies and thus remain prone to second attack with the virus. However, the role of cell mediated Immunity (CMI) needs to be studied to understand the plausibility of reinfections in sero-negative individuals,” she said.

Thus, vaccination needs to be given in individuals despite their past history of natural infection, the report added.

”Since 65 per cent of the household contacts remained asymptomatic for around a month despite testing positive through the RT-PCR method. This means early testing, even if the contacts do not develop symptoms, is mandatory to prevent the spread of the virus,” Dr Sharma said.