Viral load comparison between SARS-CoV-2 symptomatic and asymptomatic patients during the course of COVID-19 infection

Abstract

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), a novel respiratory virus is the etiological factor of COVID-19 disease which started in the Wuhan Province, China in December of 2019. Symptoms include a dry cough, fever and tiredness/fatigue while less common signs include sore throat, aches, loss of taste or smell, diarrhoea, discolouration of fingers or toes, conjunctivitis, a rash on skin, or headache. Some infected people do not develop symptoms and are therefore asymptomatic. There is inadequate information about the viral loads and transmission in asymptomatic individuals infected with SARS-CoV-2 in Zimbabwe. The virus is reported to be transmitted at the onset of symptoms by symptomatic individuals but asymptomatic individuals have the same potential to transmit the virus. The aim of the study therefore was to compare the viral loads of symptomatic and asymptomatic Zimbabwean participants during the course of COVID-19 infection. This study was approved by the Medical Research Council of Zimbabwe (MRCZA/2646). A total of 176 participants both symptomatic and asymptomatic cases of 88 individuals each were enrolled randomly from communities of the Harare province matched by gender. Rapid Detection Tests were used to initially test for positive cases and group them into symptomatic and asymptomatic cases. Nasopharyngeal swabs of positive individuals were taken, and viral RNA was extracted from the swabs using bioMérieux NucliSENS easyMag with the magnetic silica technology for extraction. Real Time RT-PCR was used to amplify the SARS-CoV-2 genetic material and obtained Ct values for each sample. Ct values were converted to viral loads using the equation of the line, y= mx + c. Viral loads were analysed in SPSS. Mann-Whitney U’s test was used to compare the relationship between symptomatic and asymptomatic viral loads. Chi square ((ꭓ2) test was used to determine the relationship between viral loads and age, gender, residency and whether one was a contact of a positive case or not. The ages of enrolled participants ranged from 16 to 99 years. Of the 176 participants 44 resided in Harare rural, 53 Chitungwiza, 20 in Epworth and 59 in Harare urban. The symptomatic group encompassed those experiencing fever (91%), chills (76%), a dry cough and loss of taste or smell (64%), tiredness/fatigue (61%), sore throat (16%), difficulties in breathing (15%), malaise (9%), body and muscle aches (6%), vomiting (3%), and chest pains and diarrhoea (2%). The mean viral loads for symptomatic and asymptomatic participants were 2.64 (0.74SD) log10 copies per 1000 cells and 2.48 (0.69SD) log10 copies per 1000 cells, respectively and there was no significant difference in mean viral loads between symptomatic and asymptomatic participants (Mann-Whitney U test p=0.079, U=3279.5). There was no significant relationship between viral loads of symptomatic and asymptomatic participants grouped by gender (ꭓ2 p=0.773; Fisher’s exact test p=0.778) and participants who either contact with positive cases or not (ꭓ2 p=0.468). There is a significant relationship between viral loads of participants grouped by age (ꭓ2 p=0.001) and by residency (ꭓ2 p=0.001). There was no significant difference in the mean viral loads between symptomatic and asymptomatic participants. Viral loads were not affected by gender or by whether one had contact with a positive case or not. Age and residency affected viral loads in participants of different age groups. In conclusion, viral loads of symptomatic and asymptomatic individuals had no significant difference. Although there was a trend that asymptomatic individuals’ viral loads were slightly lower than those of symptomatic ones, the asymptomatic individuals equally transmit the SARS-CoV-2 virus.