A senior Australian politician arrived in Australia from the United States (US) carrying a SARS-CoV-2 infection. Many infected travellers are arriving from the US at the moment. He self-reports becoming ill on Friday 13th March (AEST) and as part of his duties, had been in contact with other senior politicians prior to that. So why aren’t all those people being tested and told to self-isolate? Let’s explore some timelines and facts.
A Ministerial timeline
The official, Home Affairs Minister Peter Dutton, had been in the US. He was in a meeting in Washington on March 6. He returned to Australia March 8. He opened the University of Sunshine Coast Moreton Bay Campus March 9.[5,6] After returning to Australia, the Minister self-reported a sore throat and temperature on Friday the 13th of March.
There might be a spanner in these works. Senator Derryn Hinch tweeted that he had heard that a Federal Minister was a confirmed COVID-19 case, a day earlier on March 12 (Thursday).
On Tuesday March 10 the Minister took part in a cabinet meeting with senior members of Australia’s government and its Chief Medical Officer.[2,3]
All of that maps out as below.
The incubation and infectious periods
The time between being infected and showing signs (obvious illness like coughs and sneezes) and symptoms (the things we feel like being tired, or a headache) is called the incubation period. In that space of time, the virus is establishing its beachhead in our cells and tissues and our body is amplifying its response to that invasion. For SARS-CoV-2, the incubation time is between 2 to 14 days.
The time when we are shedding enough infectious virus that our normal interactions with other people are a risk to them and may potentially infect them is called the infectious period. This is different from the incubation period. For SARS-CoV-2, the infectious period is thought to be about 24 hours before the symptomatic period, when signs and symptoms develop.
Experts like those at the Communicable Diseases Network of Australia (CDNA) chose numbers based on evidence, the precautionary principle and sometimes hard choices. A lot of things still aren’t known about COVID-19 but you have to draw some lines in the sand because ohhhh so many things hinge on definitions. Without guidelines and definitions in the early days of an outbreak, chaos reigns supreme.
Public health experts develop definitions for all aspects of an emerging or re-emerging disease of interest. For example, the case definition lists the things that lead us to suspect an ill person could be a suspect case of the disease and the steps required to either convert that person into a confirmed case or a non-case. These experts and their advisory colleagues also define what the infectious period is, who should be tested and when and how to investigate suspect cases. They explain how to gather important information, highlight infection control considerations and outline case and contact management. Among other things. Experts also define “contact” between an infected person and uninfected people. All done by looking at the evidence in hand and the history of related events.
Contact and infectious period
Once someone is infected, we can look to the infectious period to provide us with a measure of the risk to anyone who came into suitable contact with that person – was it close contact, prolonged contact, causal and so on?
How long before becoming symptomatic, can a COVID-19 case shed virus?
We don’t know this with 100% certainty – welcome to biology – so a line has been drawn.
In Australia, we have defined the period before an infected person shows any signs of COVID-19, when they might be shedding infectious virus, as being the preceding 24 hours. So if someone came into suitable contact with an infected person, say, 48 hours before that person showed signs of illness, the contact would not be defined as a close contact. Also, if someone was wearing appropriate personal protective equipment (PPE), they aren’t considered a close contact even if the person is showing signs of disease.
How long after the onset of illness does a COVID-19 case shed virus for?
This varies between mild and severe cases. We know that among those who die, virus genetic material can be detected up until the end of life. Those who survive may shed virus genetic material for weeks after they are clinically well. Presymptomatic, mild and asymptomatic cases (called cases because these were still laboratory-confirmed infections) can shed detectable virus genetic material for up to three weeks in respiratory specimens.[9,10]
What does all this mean for the Minister?
The Minister was unlikely to be shedding infectious virus to have been a risk to others he met with during the days before that 24-hour window.
The magic 24-hour figure will continue to be watched though. And should evidence appear suggesting the presymptomatic period is greater than 24 hours, I’m sure it will be adjusted accordingly.
In the meantime, for some context, most of Australia’s COVID-19 cases have had links to infected travellers, mostly from the United States. Despite this, we haven’t seen large numbers of contacts who sat within two rows or seats of an often presymptomatic case, become ill. Sometimes – in all the noise and news – it’s hard to see that the virus does need some time, some symptoms and some proximity to spread.
- Clinical course and risk factors for mortality of adult inpatients with COVID-19 in Wuhan, China: a retrospective cohort study
- Clinical characteristics of 24 asymptomatic infections with COVID-19 screened among close contacts in Nanjing, China
- SARS-CoV-2 Viral Load in Upper Respiratory Specimens of Infected Patients
- Coronavirus Disease 2019 (COVID-19) | CDNA National guidelines for public health units