COVID-19 Testing, Travel, and Risk factors

CORONA Virus Map

July 2, 2020

The New Epicenter

In the last few weeks, the United States has become the epicenter of the pandemic. South America, and specifically Brazil, appear to be the hardest-hit country at present, but the southern United States is clearly seeing new peaks in the disease.

The first U.S. peak was in late April with 36,000 cases per day. On June 26, a new peak was reached at 47,000 cases in 1 day. In the last 4 days, the case count declined back to about 42,000 cases per day. We cannot say that we have passed another peak, but this decrease of more than 10% is a good sign.

Seven states have recorded their highest levels of hospitalization. However, the number of hospitalizations is not equivalent to the number of patients hospitalized. Florida for example has seen record numbers of hospitalizations but simultaneously reports more bed and ICU capacity. This reflects both the younger range of the patients being hospitalized, and the relative effectiveness of treatment for the most ill patients.

Importantly though, case numbers do not tell the whole story. Deaths per day in the United States peaked at about 2,800 on April 22, but as of yesterday deaths were about 280/day and continuing to drop. The two key factors related to this difference are the much younger age of the population infected, and that the at-risk members of society have recognized the importance of taking measures to be protected.


Please remember that antibody testing can never be used to determine the presence or absence of disease, only PCR testing with nasal or throat swabs or saliva can do that. The most accurate machines for performing the testing continue to be the large laboratory-based machines. The point-of-care testing machines are only useful for proving the presence of disease when symptoms already make that highly likely. A point-of-care test should generally not be used to prove someone is noninfectious, and, a laboratory-based negative only gives an indication that someone is noninfectious for the 2 full days following the test. Note that this does not help much if the test takes 48 hours to return as is commonly the case. The issues with unacceptably high false-negative rates are still there.

Some interesting data is developing from around the world related to antibodies. In the United States, the Centers for Disease Control and protection stated they believe that approximately 6% of the population has been infected at some point with COVID-19. In New York City, this number is believed to be over 20%. However, 20% is only about one-third of what is required to reach herd immunity.

Antibody testing data continues to show that most people who were ill and documented as COVID-19 positive do develop antibodies. Multiple studies demonstrate that the number of antibodies is proportional to the severity of the illness, but more research is needed to know whether this equates to a greater degree of immunity for people who were more ill.

Most authorities continue to note that a time and symptoms-based strategy for returning to work after having COVID-19 is more accurate and effective than requiring PCR testing. This is because many people will continue to test PCR positive for many days after they are no longer infectious. The current standard is to allow people to return to work and other activities 10 days after the start of symptoms as long as the last 3 days are symptom-free. For people who have positive tests without the development of symptoms, the 10-day clock should start on the day the test is taken.

Saliva-based testing has been shown to have accuracy acceptably comparable to swab-based technologies. Saliva-based tests still need to be run on large laboratory-based equipment and not on office-based machines. Additionally, the accuracy of saliva-based tests is greatly enhanced by using a sample taken in the morning.

Finally, the US equal employment opportunity commission has weighed in on what tests are acceptable in a work environment. The EEOC has said that PCR-based testing is completely acceptable as the purpose is to protect the workforce in general. Antibody testing is primarily targeted at information for the individual, and based on current CDC guidelines, cannot be used for making risk determinations related to work. Therefore, the EEOC has ruled that antibody testing cannot be a mandatory part of a workplace health program.

Risk Factors

The World Health Organization and the US CDC have provided some additional clarity on diseases that do appear to be associated with increased severity of COVID-19. Only four issues have been clearly associated with higher risk factors. These diseases are:

  • Serious heart disease
  • Chronic kidney disease
  • Obesity defined as a body mass index of greater than 30
  • Type 2 diabetes mellitus

Other diseases that were initially felt to be indicators of higher risk have not been shown to be such indicators. Importantly this does not mean that the second group of diseases is risk-free but only that there is a much less clear risk association. These diseases include:

  • Asthma
  • Hypertension
  • Pregnancy
  • History of smoking
  • Immune deficiency diseases
  • Liver disease
  • Type 1 diabetes mellitus.


Many people and organizations are looking for guidelines on which destinations have a higher risk, and when travelers should take special precautions on return from trips. When it comes to travel, three different categories of factors need to be considered.

The first is if the travelers have a preexisting condition that puts them at high risk. High-risk travelers should continue to carefully rethink travel to areas with greater than community transmission. There is no universal agreement on levels of risk associated with the destination, a useful rule is the number of cases per million per week.

Consider locations with less than 200 cases per million per week as being relatively low risk. Locations with 200-350 cases per million per week as medium risk. Locations with greater than 350 cases per million per week as the highest risk travel destinations. This risk should also be modified by consideration of the activities that a traveler will engage in.

Activities that include very limited contact with the local population such as staying at a private vacation home or hiking greatly mitigate any location-based risk. Activities such as visiting bars and nightclubs would indicate a higher level of risk than the baseline destination risk.

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