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

Abstract

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.

Keywords: COVID-19; Egypt; SARS-CoV-2; cruise travel.

Figure 1.

States of residence for 149 primary cases and 15 secondary, tertiary and quaternary cases associated with Nile River cruise travel. A detailed contact investigation was conducted in Wisconsin, resulting in the identification of more community transmission events.

Figure 2.

Epidemic curve of symptom onset date for primary and secondary, tertiary, and quaternary cases associated with Nile River cruise travel. Symptom onset date was available for 133 primary cases (missing for 16) and 13 secondary/tertiary/quaternary community cases (missing for 2 cases).

Figure 3.

Phylogenetic tree including sequences from Nile River cruise travellers returning to the USA (n = 82), sequences from Egypt (n = 1), Japan (n = 10) and Taiwan (n = 1). Global background sequences are shown in grey. Sequences were only available for 82/164 primary and community cases associated with Nile cruise travel.

Figure 4.

Phylogenetic tree of sequences from Nile River cruise travellers (n = 69), organized by voyage. Among the 82 Nile River cruise travellers, vessel information was not available for 13 people