Severe acute respiratory syndrome coronavirus 2 prevalence in 1170 asymptomatic Norwegian conscripts

Accurate estimates of SARS-CoV-2 infection in different population groups are important for the health authorities. In Norway, public infection control measures have successfully curbed the pandemic. However, military training and service are incompatible with these measures; therefore extended infection control measures were implemented in the Norwegian Armed Forces. We aimed to describe these measures, discuss their value, and investigate the polymerase chain reaction (PCR) prevalence and seroprevalence of SARS-CoV-2, as well as changes in antibody titer levels over the 6-week military training period in a young, asymptomatic population of conscripts.

In April 2020, 1170 healthy conscripts (median age 20 years) enrolled in military training. Extended infection control measures included a pre-enrollment telephone interview, self-imposed quarantine, questionnaires, and serial SARS-CoV-2 testing. At enrollment, questionnaires were used to collect information on symptoms, and SARS-CoV-2 rapid antibody testing was conducted. Serial SARS-CoV-2 PCR and serology testing were used to estimate the prevalence of confirmed SARS-CoV-2 and monitor titer levels at enrollment, and 3 and 6 weeks thereafter.

At enrollment, only 0.2% of conscripts were SARS-CoV-2 PCR-positive, and seroprevalence was 0.6%. Serological titer levels increased nearly 5-fold over the 6-week observation period. Eighteen conscripts reported mild respiratory symptoms during the 2 weeks prior to enrollment (all were PCR-negative; one was serology-positive), whereas 17 conscripts reported respiratory symptoms and nine had fever at enrollment (all were PCR- and serology-negative).

The prevalence of SARS-CoV-2 was less than 1% in our sample of healthy Norwegian conscripts. Testing of asymptomatic conscripts seems of no value in times of low COVID-19 prevalence. SARS-CoV-2 antibody titer levels increased substantially over time in conscripts with mild symptoms.