Costa Rica’s rising coronavirus numbers aren’t simply due to more testing

Costa Rica has averaged 251 new coronavirus cases daily over the last 10 days, by far its largest increase during the pandemic.

The country is indeed testing more people than before. So far in July, Costa Rica averages 1,084 daily tests (through July 6), up from 277 daily tests over the last half of April.

At the same time, Costa Rica’s test-positivity rate has increased dramatically (i.e., out of all people tested, how many came back positive). This is shown by the red line on the above graph, which represents a seven-day moving average.

Hospitalizations on the rise

Meanwhile, Costa Rica is experiencing a rise in COVID-19 hospitalizations. While many of those who test positive for the coronavirus are asymptomatic (or have mild symptoms), more people are currently hospitalized with COVID-19 than ever before:

Why has Costa Rica’s test-positivity rate increased?

Costa Rica’s test-positivity rate has increased because there are many more people with the coronavirus today than there were in April, according to Mario Ruíz, medical manager of the Social Security System (CCSS).

“There is higher circulation of the virus, and higher chances of contagion,” Ruiz said of the positivity rate.

That’s likely due to various factors, including an easing of restrictions, people breaking physical-distancing guidelines, undocumented migration, and a strain of the coronavirus that is more contagious than the one that first appeared in China last year.

At the same time, Costa Rica has improved at targeting testing. For instance, health authorities conducted mass testing in Pavas after detecting traces of the SARS-CoV-2 virus in the district’s wastewater.

The CCSS is now testing at least 1,800 people in Alajuelita.

What does it mean to have high test positivity?

According to Johns Hopkins:

If a positivity rate is too high, that may indicate that the state is only testing the sickest patients who seek medical attention, and is not casting a wide enough net to know how much of the virus is spreading within its communities. A low rate of positivity in testing data can be seen as a sign that a state has sufficient testing capacity for the size of their outbreak and is testing enough of its population to make informed decisions about reopening. 

The World Health Organization (WHO) says that a test-positivity rate below 5% for two weeks is one indication a country has controlled the epidemic.

How did we calculate test-positivity rate?

We first calculated the daily number of people tested by adding a day’s new positive cases to new people who tested negative. (This is typically lower than the total number of new tests performed in a day, since one person can be tested several times.)

We then found the average percentage of tests that were positive over the prior seven days.

Here’s the raw data: