Infectious Disease Prevention: PCR Testing For Holiday Gatherings

Dr. Janie French • Nov. 25, 2024

As we enter the holiday season, many of us will look forward to gatherings with loved ones. Simultaneously, respiratory season will be upon us, contributing to common respiratory symptoms such as congestion, cough, sore throat, fever, and fatigue. For some people, like infants and elderly people, common respiratory infections can cause severe disease, including pneumonia. To help make gatherings as stress-free as possible, keeping everyone healthy is key.

The first step to staying healthy is to identify risk and reduce that risk when possible. To reduce risk, it can be helpful to identify situations where people with active respiratory infections are going to be present. These often include daycares and hospitals. However, it’s not always possible to avoid spaces where viruses are circulating, as many people rely on public transit for holiday travel. In these cases, there may be small actions that reduce exposure risk. For example, research has identified strategies for reducing transmission during air travel [1]. Research has shown that people sitting in window seats on airplanes are less likely to develop infection when another person on the airplane is infected with a respiratory virus due to the reduced number of people they come into contact with [2]. Additionally, infection prevention tools such as handwashing and physical distancing can reduce the likelihood of developing an infection [3].

After exposure to a virus, it may take several days before symptoms appear. This delay between exposure and development of symptoms is referred to as the incubation period. During this period, the respiratory virus is beginning to replicate and spread in the respiratory tract. Viruses differ in their incubation periods, with the omicron variant of SARS-CoV-2 (COVID-19) having an incubation period of 3.42 days [4], influenza A virus having an incubation period of 1.4 days [5], and respiratory syncytial virus (RSV) have an incubation period of 4.4 days [5]. Given the delay in development of symptoms, it’s possible to be infected and releasing virus into the environment without being aware of it. So, reducing exposure to people with respiratory symptoms in the days leading up to family gatherings can reduce the risk of unknowingly spreading infection among loved ones.

During these incubation periods, even though a person is infected with the virus, a test to identify infection may result as negative because the amount of virus may be insufficient to be detectable by the test. For COVID-19, if a person has a known exposure to someone infected with the virus, the CDC recommends testing at least five full days after exposure if you don’t have any symptoms [6]. Testing can be done with either a nucleic acid amplification test, like PCR, or with an at-home rapid antigen test [6]. However, if rapid antigen tests are used, the CDC recommends repeat testing two days after the initial negative result [6]. For other respiratory viruses, like influenza virus, the CDC recommends testing only if symptoms develop [7]. For patients at average risk of influenza complications, testing as soon as symptoms develop may mean that you are eligible to receive treatment with an antiviral medication if the test is positive for influenza virus, as guidelines from the Infectious Diseases Society of America (IDSA) recommend antiviral treatment if illness onset is within two days of presentation [8]. Influenza antivirals can shorten symptom duration by an average of one day, to help you feel better faster. Additionally, antigen tests are less effective when used more than four days after symptom onset, as viral shedding in the respiratory tract decreases after three to four days after symptoms develop in most people [9]. So testing sooner means more accurate test results.