In the last few days, Italy’s reported cases has continued to rise despite the quarantine. There have been plenty of people asking me about it, so I figured I’d explain what I understand about the situation.
To begin with, what is meant by “reported cases”? Sounds simple, right? You have someone who has tested positive for the virus, and that person is then included in the country’s tally. Here’s what has to happen for that:
1. There has to be a reason to test the person
2. There has to be a test available
3. The person has to test positive
Let’s talk about these elements, because they make a big difference from country to country. Having good data is arguably fundamental to understanding the spread and behavior of an illness, but when there are large number of reported cases (even if mild), that can lead to panic in the population and/or problems for politicians. Statistics and data are often muddied by those issues.
1. Reason to test the person. In Italy, they have been ramping up the numbers of tests, particularly in communities like Todi. As the mayor explained, as a case has tested positive, they have gone out of their way to identify ALL contacts within the past 5-7 days, and test those people as well. That way, any further positives can be isolated as quickly as possible (as well as being monitored). This helps in two ways: it prevents the spread of the infection and it helps keep the patient as healthy as possible to reduce the chances that he or she will end up on ventilator. So, in Italy, the barrier to being tested is quite low. The UK and the US are going a different direction, and are testing very few people. From what I understand in the news, NY and CA are now only testing people with symptoms who are in the hospital (where it could affect their treatment), healthcare workers, and the like. Otherwise, you’re told to stay at home if you start exhibiting symptoms.
2. Available tests. Early on, the US did not have a lot of tests available, and is still having problems meeting demand (part of the reason for the declared testing protocol). Here, the test availability (and use) has gone up recently. If you don’t have tests available, you cannot even test those who meet the baseline criteria for testing.
3. Testing positive. I have no idea what level of false positives or negatives the various tests have, but I felt the need to put this in for completeness.
Common sense tells us that the more people you test, the more likely you are to find people with the virus. Since it is an illness that can have very few symptoms on a number of patients, testing people who aren’t feeling ill will still result in a certain number of cases. If you don’t test people unless they’re complaining of symptoms, you will of course miss those cases. The higher your threshold for testing, the more cases you’ll miss. Since Italy has recently ramped up its testing, it looks like the number of cases is increasing dramatically. This does not necessarily mean that the illness is now more prevalent than it was yesterday (although it could mean that). What it does mean, though, is that the people who have the illness are identified and the problem is one that can be better contained.
Countries that reduce the number of tests performed will appear to be doing a great job containing the virus, but all it means is that fewer ill people are being recognized and treated and/or prevented from making others ill. In the context of a non-quarantined society, this is important: consider someone who is still able to go to the grocery store, lives in shared housing (roommates or family members). That person comes down with covid-19, and maybe stays in bed. In the meantime, the housemates continue to go out an about with possibly contaminated clothing, and possibly ill themselves.
In a quarantined society, arguably greater testing confers little additional benefit, but that’s in the case of 100% quarantine. Here in Italy, we’re allowed to shop and take care of necessities. However, once a household has an incidence of covid-19, they are on 100% quarantine and food and supplies are brought to them. This allows a halfway (cheaper) quarantine, since you are actually allowed to leave your house for limited purposes.
Does this cost money? Absolutely. However, treating very ill people also costs a significant amount, and the goal here is to minimize as much as possible human suffering and the concomitant costs of the contagion. Cost of testing is certainly a downside to having an extensive testing regimen. Who can say accurately at this point how the cost of testing balances out with reduced mortality overall?
Bottom line is: the numbers are important. Understanding how to compare and evaluate these numbers across the world and over time even in the same country is critical. Headlines are there to give readers an idea what is happening in broad terms, but unless an article addresses how the tests are being performed and what changes might have occurred to the testing protocol, don’t put too much faith in the conclusions that the author (or you!) might draw from these numbers.
A great example is China’s history. If you look at their graphs, at some point in February, they changed the diagnosis or testing criteria to be a lot looser. Their cases (surprise surprise) appeared to grow dramatically. They changed those criteria back to what they had been, and suddenly the curve became consistent and predictable.
(Yes, I might be following the statistics a little too closely)
Love,
Alexandra
To begin with, what is meant by “reported cases”? Sounds simple, right? You have someone who has tested positive for the virus, and that person is then included in the country’s tally. Here’s what has to happen for that:
1. There has to be a reason to test the person
2. There has to be a test available
3. The person has to test positive
Let’s talk about these elements, because they make a big difference from country to country. Having good data is arguably fundamental to understanding the spread and behavior of an illness, but when there are large number of reported cases (even if mild), that can lead to panic in the population and/or problems for politicians. Statistics and data are often muddied by those issues.
1. Reason to test the person. In Italy, they have been ramping up the numbers of tests, particularly in communities like Todi. As the mayor explained, as a case has tested positive, they have gone out of their way to identify ALL contacts within the past 5-7 days, and test those people as well. That way, any further positives can be isolated as quickly as possible (as well as being monitored). This helps in two ways: it prevents the spread of the infection and it helps keep the patient as healthy as possible to reduce the chances that he or she will end up on ventilator. So, in Italy, the barrier to being tested is quite low. The UK and the US are going a different direction, and are testing very few people. From what I understand in the news, NY and CA are now only testing people with symptoms who are in the hospital (where it could affect their treatment), healthcare workers, and the like. Otherwise, you’re told to stay at home if you start exhibiting symptoms.
2. Available tests. Early on, the US did not have a lot of tests available, and is still having problems meeting demand (part of the reason for the declared testing protocol). Here, the test availability (and use) has gone up recently. If you don’t have tests available, you cannot even test those who meet the baseline criteria for testing.
3. Testing positive. I have no idea what level of false positives or negatives the various tests have, but I felt the need to put this in for completeness.
Common sense tells us that the more people you test, the more likely you are to find people with the virus. Since it is an illness that can have very few symptoms on a number of patients, testing people who aren’t feeling ill will still result in a certain number of cases. If you don’t test people unless they’re complaining of symptoms, you will of course miss those cases. The higher your threshold for testing, the more cases you’ll miss. Since Italy has recently ramped up its testing, it looks like the number of cases is increasing dramatically. This does not necessarily mean that the illness is now more prevalent than it was yesterday (although it could mean that). What it does mean, though, is that the people who have the illness are identified and the problem is one that can be better contained.
Countries that reduce the number of tests performed will appear to be doing a great job containing the virus, but all it means is that fewer ill people are being recognized and treated and/or prevented from making others ill. In the context of a non-quarantined society, this is important: consider someone who is still able to go to the grocery store, lives in shared housing (roommates or family members). That person comes down with covid-19, and maybe stays in bed. In the meantime, the housemates continue to go out an about with possibly contaminated clothing, and possibly ill themselves.
In a quarantined society, arguably greater testing confers little additional benefit, but that’s in the case of 100% quarantine. Here in Italy, we’re allowed to shop and take care of necessities. However, once a household has an incidence of covid-19, they are on 100% quarantine and food and supplies are brought to them. This allows a halfway (cheaper) quarantine, since you are actually allowed to leave your house for limited purposes.
Does this cost money? Absolutely. However, treating very ill people also costs a significant amount, and the goal here is to minimize as much as possible human suffering and the concomitant costs of the contagion. Cost of testing is certainly a downside to having an extensive testing regimen. Who can say accurately at this point how the cost of testing balances out with reduced mortality overall?
Bottom line is: the numbers are important. Understanding how to compare and evaluate these numbers across the world and over time even in the same country is critical. Headlines are there to give readers an idea what is happening in broad terms, but unless an article addresses how the tests are being performed and what changes might have occurred to the testing protocol, don’t put too much faith in the conclusions that the author (or you!) might draw from these numbers.
A great example is China’s history. If you look at their graphs, at some point in February, they changed the diagnosis or testing criteria to be a lot looser. Their cases (surprise surprise) appeared to grow dramatically. They changed those criteria back to what they had been, and suddenly the curve became consistent and predictable.
(Yes, I might be following the statistics a little too closely)
Love,
Alexandra
No comments:
Post a Comment
We love to hear your comments! They encourage us to write more!!