Epidemiology of Covid-19

Abstract

We provide a summary of various epidemiological parameters related to COVID-19 such as incubation period, serial interval and other parameters. Understanding these parameters is important for developing prevention strategies. SARS-CoV-2 can be transmitted by droplets and close contact, but there is evidence of airborne transmission. Aerosol-generating procedures have been identified as one of the specific risk factors for healthcare workers. Super-spreading events refer to situations where a small number of individuals cause the majority of infections. The basic reproductive number (R0) and the spread parameter (k) are used to characterise the transmissibility of the disease. Estimated values for R0 range from 2 to 3 and the estimated value for k is 0.1.The duration of infectiousness depends on viral load and shedding. Viral load varies according to factors such as clinical spectrum, type of variant and vaccination status. The relationship between viral load and infectivity is not fully understood.With regard to the frequency of symptoms and signs of COVID-19, fever, cough, fatigue and dyspnoea are common. The prevalence of olfactory and gustatory dysfunction (OGD) varies between studies and countries. Age and comorbidities are factors associated with olfactory dysfunction.Estimates of the proportion of asymptomatic patients range from 6% to 96%. Asymptomatic transmission is considered likely and is important for control measures.We reviewed the quantitative semiology of COVID-19 is reported on sensitivity, specificity and likelihood ratios of signs.Finally, we also review risk factors for COVID-19 (including health care workers), co-infections, and epidemiology of variants..