Symptoms and transmission of COVID-19

By Dr Stephen Ritchie, Infectious Disease Expert

3 April 2020

COVID-19, the illness caused by the SARS-CoV-2 virus, is an illness primarily characterised by a fever and cough. Most of the clinical information about coronavirus has come from China, particularly Wuhan.

In Wuhan, most people diagnosed with coronavirus were admitted to hospital, regardless of the severity of their illness. Very little is known about the clinical features of people who had very mild symptoms (more than 80 percent of total  cases), many of whom may not have sought medical consultation.  

Symptoms

The clinical information about Chinese coronavirus cases is likely to have included more cases at the severe end of the disease spectrum. The mean time from symptom onset following exposure was 7.1 days (95 percent confidence intervals, 6.1-8.1 days)1.

A wide range of symptoms other than fever and cough have been reported; the table below shows the symptoms of 55,924 patients with laboratory confirmed coronavirus2. Notably, nasal congestion was an uncommon symptom, but it is not possible to tell whether nasal congestion occurred in isolation or in combination with cough and fever.

A study of Chinese patients with mild coronavirus and gastrointestinal symptoms (all laboratory confirmed, with no organ dysfunction and no requirement for oxygen therapy) found that in 19 percent of these cases their gastrointestinal symptoms preceded their respiratory symptoms. Anosmia (and loss of taste) is an interesting symptom commonly reported in the media in people with mild disease, which appears to resolve spontaneously as coronavirus resolves.

Table. The proportion of 55,924 Chinese patients who had various symptoms of coronavirus.

Fever 88% 
Dry cough 68%
Sputum production 33%
Dyspnoea 19%
Sore throat 14%
Headache 14%
Myalgia, aches and pains 15%
Chills 11%
Nausea and vomiting 5%
Nasal congestion 5%
Diarrhoea 4%

Transmission

Respiratory viruses are usually spread by contact and by droplets generated by coughing and sneezing. Droplets fall with gravity and don’t usually travel in air for more than one to two metres. Some respiratory viruses can float like dust and remain suspended in air for short periods of time; they can be “airborne”. Influenza is spread via contact and droplet routes; measles is spread via contact, droplet and airborne routes.

Coronavirus is transmitted via contact and droplets produced by symptomatic patients. Airborne transmission was not suspected in analysis of 75,465 COVID-19 cases form China reported to the World Health Organisation2. A study of the hospital environments of patients in Singapore found environmental contamination with SARS-CoV-2, but the virus was not detected in any of the air samples – it did not float like dust3.

Early in the coronavirus epidemic in China, it was reported that asymptomatic people were able to transmit disease , but this report was incorrect and there is no convincing evidence that asymptomatic people really transmit coronavirus. However, a recent mathematical modelling study postulated that people with mild, undiagnosed disease caused a lot of the coronavirus transmission during the epidemic in Wuhan5.

It is difficult to determine just how infectious coronavirus really is, and how it compares to other viruses like influenza. In China, five to 10 percent; of household contacts of people with coronavirus became infected2; in Shenzhen, 2.8 percent of people undergoing contact tracing became positive for coronavirus, and in Sichuan Province, 0.9 percent of contacts of 23,178 cases became positive2
Epidemiologists use the term “reproductive number” (R) to indicate how many people, on average, are infected by each person with coronavirus. In Wuhan in early February, the value of R was between two and three (similar to influenza)5, but with concerted public health measures (e.g. quarantine, contact tracing, “lockdown”) R reduced to <1 and the epidemic waned. We are all hoping that current efforts to control coronavirus in New Zealand will keep R<1 and avoid a widespread epidemic.

 

References 

  1. Zhao, et al. Incidence, clinical characteristics and prognostic factor of patients with COVID-19: a systematic review and meta-analysis; (pre peer review) https://www.medrxiv.org/content/10.1101/2020.03.17.20037572v1.
  2. Report of the WHO-China Joint Mission on Coronavirus Disease 2019; https://www.who.int/docs/default-source/coronaviruse/who-china-joint-mission-on-covid-19-final-report.pdf.
  3. Ong et al. Air, Surface Environmental, and Personal Protective Equipment Contamination by Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) From a Symptomatic Patient. JAMA 2020; doi:10.1001/jama.2020.3227.
  4. Rothe et al. Transmission of 2019-nCoV Infection from an Asymptomatic Contact in Germany. NEJM 2020; 382:970-1.
  5. Li et al. Substantial undocumented infection facilitates the rapid disseimination of novel coronavirus. Science 2020; 10.1126/science.abb3221