A healthcare worker tests Eric Rodriguez with a nose swab on July 22, 2020 at a pop-up test site at the Koinonia Worship Center and Village in Pembroke Park, Florida on COVID-19.
Joe Raedle | Getty Images
While the number of coronavirus cases is increasing in the U.S., President Donald Trump continues to blame the tests – at rallies, interviews, and on Twitter – for the recent increase in the outbreak.
"If we weren't testing, you wouldn't be able to show this chart," Trump replied to a question from Chris Wallace about rising US Covid 19 cases in a Fox News interview that aired on July 19 tested a lot, these numbers would have dropped. "
However, a CNBC analysis of the test data showed that despite the increase in test capacity in the United States, cases of the virus are found more frequently. This pattern contradicts what epidemiologists say when a country gets a pandemic under control.
"This claim is obviously wrong," said Dr. Yonatan Grad, professor of immunology and infectious diseases at Harvard, in response to the idea that intensified tests explain the recent outbreak. "It is misleading at best and, at worst, intentionally undermines responses to public health."
In interviews with CNBC, epidemiologists referred to the "percentage of positive tests" to understand whether the growth of US coronavirus cases was solely due to increased tests. When corona virus tests are in short supply, usually only the sickest people are tested, which means that the proportion of positive tests in the overall tests is high. However, as more tests become available, those with mild or no symptoms – who are less likely to have Covid-19 – can receive tests that would result in a lower positive rate if the virus did not spread.
According to a CNBC analysis of data from the Covid Tracking Project, the percentage of positive tests in the US rose from 5.4% on Memorial Day to 8.6% on 23. July increased. Nationwide daily tests almost doubled during this period, from an average of 410,000 daily tests on May 25th to more than 775,000 daily tests on July 23rd. To account for daily fluctuations in reporting, the CNBC analysis used a 7-day average of cases and tests to calculate the percentage positive rates.
The World Health Organization has stated that in countries that have undergone extensive testing for Covid-19, the percentage positive rate should remain at 5% or less for at least 14 days.
"If the disease does not spread and you do more tests, the positive fraction should remain stable or decrease," said Dr. Degree versus CNBC. "But in fact we see that the proportion of positive tests increases with increasing tests. This is a clear indication that the virus is spreading more and more."
Twenty-nine states have seen their percentage positive rates increase since Memorial Day, and this trend is also true for the countries with the largest virus outbreaks. In each of the ten countries where the majority of coronavirus cases occurred between May 25 and July 23, the percentage of positive tests also increased during this period.
Of these ten states, none had more positive increases than Arizona. On May 25, the rate of positive tests in the state was 7.6%, which is equivalent to 25% as of July 23. During this period, Arizona reported more than 136,000 new coronavirus cases, according to data from the Covid Tracking Project.
In California, more than 331,000 cases have been reported since Memorial Day, as the percentage positive rate of the state has doubled from 4% to 8%. Dr. Julie Vaishampayan, the health officer in Stanislaus County east of San Jose, told CNBC that her area had been particularly badly affected in the past few weeks and that attributing the increase in reported coronavirus cases to further testing is not the whole story of the outbreak.
"The more tests you do, the more cases you can actually identify," said Dr. Vaishampayan when asked if increasing the tests was the cause of the increase in the number of cases. "But that's not the whole truth."
Dr. Vaishampayan said that as their county expanded its testing capacity, the percentage positive rate also increased from 3% to 20%. "We do more tests, but we find a lot more positives," she said.
The percentage positive rate can be affected by the type of populations tested. If existing test resources were provided for vulnerable populations, e.g. B. Nursing homes where viruses break out would likely see a higher proportion of positive test results. But at least in Stanislaus County, Dr. Vaishampayan that they "didn't change anything at the test sites" which would of course affect the percentage positive rate and believes that this is also the case at the state level.
Epidemiologists also emphasized the importance of examining multiple metrics to track the spread of Covid-19, including hospitalizations and deaths. And testing, even if it contributes in part to higher official case numbers, is critical to Covid-19's response to public health.
"More tests are good," said Dr. Lorna Thorpe, professor of epidemiology at New York University. "From a public health perspective, the more cases we know, the better. We want to know about cases so that they can be treated and isolated, and try to stop the transmission."