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(Act. May 18, 2020 6:08 PM)
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So far 890 Vorarlbergers have tested positive.
© Steurer / Pixabay
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“The infected people are all now in quarantine,” has been heard many times in the past few days when it comes to the question of whether it still makes sense to reduce contacts. But the fact is: of the five Vorarlbergers who tested positive last Thursday, three do not know where they got Covid-19.
As the state announced on VOL.AT request, five people in Vorarlberg have tested positive for the corona virus since May 14. Two of them had confirmed contact with a sick family member. The remaining three don’t know where and how they got infected. You may have contracted an asymptomatic acquaintance or an infected stranger, in this case it is difficult to trace the origin of the infection. It would be immensely important to identify contacts so that they cannot spread the disease any further.
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Claudia from Hohenems, who became infected with the virus in mid-March, was only able to speculate in an interview with VOL.AT about where she might have caught the virus.
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Interview with Claudia from Hohenems
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Cluster analysis and contact tracing against “second wave”
The Austrian authorities rely on cluster analyzes and contact tracing to ensure that the uncontrolled “second wave” does not occur after relaxing the measures against the new type of corona virus. Because infected people can infect others before symptoms begin, the time to find an infected person is short.
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“If the serial interval – as with Covid-19 – is shorter than the mean incubation period, infected people infect more people before the onset of symptoms. This short period of time means that you have time to find the infected person and to quarantine them so that further transmissions can take place can be prevented, “explained Daniela Schmid, head of the infection epidemiology department of AGES (Austrian Agency for Health and Food Security). “We take two days before the onset of symptoms as the start of the search for contacts, as there are proven presymptomatic transmissions.” The expert was interviewed by the Science Media Center Germany (SMC) about cluster analyzes. The serial interval means the time from the beginning of the illness of one person to the beginning of the illness of another person infected by him in an infection chain.
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This is how the search for clusters works
“According to the WHO definition, a cluster is an accumulation of cases by time or place or an accumulation of cases that are characterized by a common exposure, for example a trip together, a visit to a party or a cooking course,” continued Schmid. The process of locating a cluster is as follows: “Using rapid PCR tests, we can identify a new infection, from which we then start the further analysis with classic case and contact tracing. So we look backwards for up to 14 days – the maximum incubation time after a contact, in which the case may have been infected, the primary case. From the date of the index case’s illness, we then search again two days backwards and until the case is isolated for further contacts that the identified case could have infected. These are people who cumulatively had more than 15 minutes of close contact that would have made droplet transfer possible. “
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The shortness of the serial interval at SARS-CoV-2 makes the virus so treacherous: “I simply have little time to find the contacts in the following generations before they themselves become a case and thus a spreader,” says the expert, according to the SMC .
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Duration of the disease underestimated at the beginning
With contact tracing, cases and contacts are questioned using a standardized questionnaire, when they developed symptoms and which ones. The gain in knowledge depends on the one hand on the memory of the date of illness. “On the other hand, the symptoms to be queried have also changed over time. At the beginning there were mainly dry coughs and fevers, with time there was an added lack of smell and taste, which may even appear earlier. So we initially underestimated the duration of the disease and other contacts are missing, “said Schmid. Many people also struggle to remember which activities they have undertaken, where contacts may have taken place. Before the lockdown, it was a much bigger problem.
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“Here in Austria, the government would like to have every minute rash recorded in the case numbers and assigned to a transmission chain,” SMC quoted the epidemiologist. “Germany is a bit of a role model with its special scouts for contact tracing. Such a concept is hardly possible in the local structure.” The local health structures had to be “given more support”, and one would never be able to “retrospectively assign each individual case to a cluster”. The lower the level of the current number of cases, the easier it is to assign cases to small clusters.
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