The mathematical models pointed, weeks ago, it was highly likely that the coronavirus arrived in Spain. That’s why we recommend suspending the Mobile World Congress. These models, which were right in their predictions, indicate today that the probability of the epidemic spreading in Spain is high. For two reasons: there is a drip of cases imported from Italy and we know that the virus is very transmissible.
When the number of cases in a locality exceeds three, as in Madrid or Valencia, the probability of a local outbreak is greater than 60%. The numbers, again, anticipate the evolution of the disease. One person can infect several: infections depend on the contacts that this person has and the time it takes to go to the hospital from the onset of symptoms. If the infection parameters are the same as in Wuhan and the prevention and control measures do not work perfectly, in Madrid there would be an increase of two cases a day in March and five daily from the first week of April. Without preventive measures, in April there would be more than 100 cases a day.
At this point, we must assess the importance of confronting native cases. When identifying a case of Covid-19, it is urgent to find out who the original cause is and follow the chain of transmission. If we succeed, we are identifying most of the cases. But, if we don’t know how to identify the patient zero, there is a transmission that is out of control.
When several cases appear in a locality and one is native – in Spain there are five -, the search must be intensified to find new cases. The question is when are we going to change the current indication of the test and start iInclude people who don’t have a travel history, and when we will systematically test all contacts, even if they have no symptoms. I think that the modification must be made right now. As soon as Health triggers this change, it will be important to look at the tests with negative results, which are an indicator of the effort that has been made to find the cases. For example, in England they have already done more than 4500 tests; us, less than 500.
A final question is to decide when a social distancing should be indicated, that is, to activate the cancellation of events to avoid crowds or the closure of schools, to reduce contagion. There is no case threshold for initiating community mitigation measures. The key indicator is that cases are not epidemiologically linked. If all (or most) of the positive patients are connected to other cases, it is a good sign, since we will be detecting and controlling the transmission chains. But if they are not linked, there is a community transmission that requires the mentioned measures. Event cancellation is recommended as of today. The decision to close schools is obviously more difficult. But it is important to do it early; If not, it does not make sense.
Oriol Mitjà He is a doctor specializing in infectious diseases at the Germans Trias i Pujol Hospital in Badalona and was the Princess of Girona prize for Scientific Research in 2013. His opinion is personal and does not have to coincide with that of his institution.