The value of contact tracing and isolation in mitigation of COVID-19 epidemic: findings from outbreak investigation of COVID-19 onboard Nile Cruise Ship, Egypt, March 2020

WHO informed Egypt health authorities of individuals of different nationalities who proved positive for COVID-19 after returning from Egypt. Patients were among touristic group who visited Cairo and spent 1-week onboard Nile cruise ship. Investigation performed to confirm outbreak, detect source, and implement containment measures. Active case finding and contact tracing performed among contacts of the index cases and their contacts. Contacts defined as anyone within 6 feet from confirmed or suspected COVID-19 case for ≥15 min. Overall, 331 contacts, including 201 ship boarders and 130 hotel guests, were listed and interviewed using semistructured questionnaire and tested for COVID-19 by PCR. Among them, 136 (41.1%) were close contacts of index cases and 195 (58.9%) contacted secondary cases. Their mean age was 34.6±11.5 years, 251 (75.8%) were males and 126 (38.1%) non-Egyptians. Of them, 67 (20.2%) tested positive for COVID-19, including 57 (28.4%) ship boarders and 10 (7.7%) hotel guests. Per cent positive was significantly higher in: contacts of index cases, Egyptians, ship boarders and in males than corresponding categories (35.3% vs 9.7%, 22.9% vs 15.9%, 27.4% vs 7.7%, 24.7% vs 6.3%), respectively. Of all positive cases, 40 (59.7%) were asymptomatic where ship boarders, non-Egyptians, >50 years old and females were more likely to be asymptomatic than corresponding categories (85.0 vs 48.9%, 72.7 vs 54.5%, 100.0 vs 56.5%), respectively. COVID-19 patients among group of tourists triggered an outbreak onboard Nile ship and hotel in Egypt. Outbreak quickly contained through lab testing, case isolation, strict infection control measures and contact tracing which proved effective in reducing COVID-19 transmission early in pandemic.