Introduction A new coronavirus, called Severe Acute Respiratory Syndrome-CoronaVirus-2 (SARS-CoV-2), has emerged from China in late 2019 and has now caused a worldwide pandemic. The impact of COVID-19 has not been described so far in a military setting. We therefore report a case series of infected patients in a recruit school in Switzerland and the herein associated challenges.

Methods Retrospective review of COVID-19 cases among Swiss Armed Forces recruits in the early weeks of SARS-CoV-2 pandemic in the canton of Ticino, the southernmost canton of Switzerland. Positive cases were defined with two positive PCR testing for SARS-CoV-2 from nasopharyngeal swabs. Serological testing was performed with a commercially available kit according to manufacturers’ instructions.

Results The first case was likely contaminated while skiing during weekend permission. He became symptomatic 4 days later, tested positive for SARS-CoV-2 and was put into isolation. He showed complete symptom resolution after 48 hours. Quarantine was ordered for all recruits with close contact in the past 2 days, a total of 55 persons out of 140 in the company. Seven out of nine recruits in one particular quarantine room became mildly symptomatic. SARS-CoV-2 PCR was positive in one of them. Seven days after initial diagnosis, the index patient and the other one from the quarantine retested positive for SARS-CoV-2, although they had been completely asymptomatic for over 96 hours. Serological testing revealed positive for both patients. All others showed negative IgM and IgG.

Conclusions Young healthy recruits often showed a mild course of COVID-19 with rapid symptom decline but were persistent SARS-CoV-2 carriers. This illustrates how asymptomatic patients may be responsible for covert viral transmission. An early and prolonged establishment of isolation and quarantine for patients and close contacts is essential to slow down the spread of SARS-CoV-2, especially in the confined space of a military environment.