COVID-19 on the Nile: a cross-sectional investigation of COVID-19 among Nile River cruise travellers returning to the United States, February-March 2020

Background Early in the pandemic, cruise travel exacerbated the global spread of SARS-CoV-2. We report epidemiologic and molecular findings from an investigation of a cluster of travellers with confirmed COVID-19 returning to the USA from Nile River cruises in Egypt. Methods State health departments reported data on real-time reverse transcription-polymerase chain reaction-confirmed COVID-19 cases with a history of Nile River cruise travel during February-March 2020 to the Centers for Disease Control and Prevention (CDC). Demographic and epidemiologic data were collected through routine surveillance channels. Sequences were obtained either from state health departments or from the Global Initiative on Sharing Avian Flu Data (GISAID). We conducted descriptive analyses of epidemiologic data and explored phylogenetic relationships between sequences. Results We identified 149 Nile River cruise travellers with confirmed COVID-19 who returned to 67 different US counties in 27 states: among those with complete data, 4.7% (6/128) died and 28.1% (38/135) were hospitalized. These individuals travelled on 20 different Nile River cruise voyages (12 unique vessels). Fifteen community transmission events were identified in four states, with 73.3% (11/15) of these occurring in Wisconsin (as the result of a more detailed contact investigation in that state). Phylogenetic analyses supported the hypothesis that travellers were most likely infected in Egypt, with most sequences in Nextstrain clade 20A 93% (87/94). We observed genetic clustering by Nile River cruise voyage and vessel. Conclusions Nile River cruise travellers with COVID-19 introduced SARS-CoV-2 over a very large geographic range, facilitating transmission across the USA early in the pandemic. Travellers who participate in cruises, even on small river vessels as investigated in this study, are at increased risk of SARS-CoV-2 exposure. Therefore, history of river cruise travel should be considered in contact tracing and outbreak investigations.