Development of a mathematical model to predict the health impact and duration of SARS-CoV-2 outbreaks on board cargo vessels

The Coronavirus Disease (COVID-19) pandemic has brought significant impact onto the maritime activities worldwide, including disruption to global trade and supply chains. The ability to predict the evolution and duration of a COVID-19 outbreak on cargo vessels would inform a more nuanced response to the event and provide a more precise return-to-trade date. This paper presents the SEIQ(H)R (Susceptibility–Exposed–Infected–Quarantine–(Hospitalisation)–Removed/Recovered) model, which is the first deterministic mathematical model developed and fit-tested to describe the transmission dynamics of COVID-19 on board cargo vessels of up to 60 crew members. Due to specific living and working circumstances on board cargo vessels, instead of utilising the reproduction number, we consider the highest fraction of crew members who share the same nationality to quantify the transmissibility of the disease. The performance of the model is verified using case studies based on data collected during COVID-19 outbreaks on three cargo vessels in Western Australia during 2020. The simulations show that the model can forecast the time taken for the transmission dynamics on each vessel to reach their equilibriums, providing informed predictions on the evolution of the outbreak, including hospitalisation rates and duration. The model demonstrates that (a) all crew members are susceptible to infection;(b) their roles on board are a determining factor in the evolution of the outbreak;and (c) an unmitigated outbreak could affect the entire crew and continue on for many weeks. The ability to model the evolution of an outbreak, in both duration and severity, is essential to predict outcomes and to plan for the best response strategy. At the same time, it offers a higher degree of certainty regarding the return to trade, which is of significant importance to multiple stakeholders.

SARS-CoV-2 infections among Australian passengers on the Diamond Princess cruise ship: A retrospective cohort study.

BACKGROUND: Prolonged periods of confined living on a cruise ship increase the risk for respiratory disease transmission. We describe the epidemiology and clinical characteristics of a SARS-CoV-2 outbreak in Australian passengers on the Diamond Princess cruise ship and provide recommendations to mitigate future cruise ship outbreaks. METHODS: We conducted a retrospective cohort study of Australian passengers who travelled on the Diamond Princess from 20 January until 4 February 2020 and were either hospitalised, remained in Japan or repatriated. The main outcome measures included an epidemic curve, demographics, symptoms, clinical and radiological signs, risk factors and length of time to clear infection. RESULTS: Among 223 Australian passengers, 56 were confirmed SARS-CoV-2 positive. Forty-nine cases had data available and of these over 70% had symptoms consistent with COVID-19. Of symptomatic cases, 17% showed signs and symptoms before the ship implemented quarantine and a further two-thirds had symptoms within one incubation period of quarantine commencing. Prior to ship-based quarantine, exposure to a close contact or cabin mate later confirmed SARS-CoV-2 positive was associated with a 3.78 fold (95% CI, 2.24-6.37) higher risk of COVID-19 acquisition compared to non-exposed passengers. Exposure to a positive cabin mate during the ship's quarantine carried a relative risk of 6.18 (95% CI, 1.96-19.46) of developing COVID-19. Persistently asymptomatic cases represented 29% of total cases. The median time to the first of two consecutive negative PCR-based SARS-CoV-2 assays was 13 days for asymptomatic cases and 19 days for symptomatic cases (p = 0.002). CONCLUSION: Ship based quarantine was effective at reducing transmission of SARS-CoV-2 amongst Australian passengers, but the risk of infection was higher if an individual shared a cabin or was a close contact of a confirmed case. Managing COVID-19 in cruise ship passengers is challenging and requires enhanced health measures and access to onshore quarantine and isolation facilities.

The Healthy Crew, Clean Vessel, and Set Departure Date Triad: Successful Control of Outbreaks of COVID-19 On Board Four Cargo Vessels.

BACKGROUND: A variety of infectious diseases can cause outbreaks on board vessels, with both health and economic effects. Internationally, Coronavirus Disease 2019 (COVID-19) outbreaks have occurred on numerous cruise and cargo vessels and the containment measures, travel restrictions, and border closures continue to make it increasingly difficult for ship operators world-wide to be granted pratique, effect crew changes, and conduct trade. An effective outbreak management strategy is essential to achieve the outcome triad - healthy crew, clean vessel, and set departure date - while maintaining the safety of the on-shore workers and broader community and minimizing disruption to trade. This report describes the principles of COVID-19 outbreak responses on four cargo vessels, including the successful use of one vessel as a quarantine facility. METHODS: Established principles of management and the experiences of COVID-19 outbreaks on cruise ships elsewhere informed a health-lead, multi-agency, strict 14-day quarantine (Q) regime based on: population density reduction on board; crew segregation; vessel cleaning and sanitation; infection risk zones, access, and control measures; health monitoring; case identification and management; food preparation and delivery; waste management control; communication; and welfare and security. FINDINGS: Sixty-five crew were diagnosed with Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) infection (range 2-25; attack rate 10%-81%; 15 asymptomatic). No deaths were recorded, and only one crew was hospitalized for COVID-19-related symptoms but did not require intensive care support. Catering crew were among the cases on three vessels. All non-essential crew (n-EC) and most of the cases were disembarked. During the vessel's Q period, no further cases were diagnosed on board, and no crew became symptomatic after completion of Q. The outbreak response duration was 15-17 days from initial decision.No serious health issues were reported, no response staff became infected, and only two Q protocol breaches occurred among crew. INTERPRETATION: Despite increasing risk of outbreaks on cargo vessels, maritime trade and crew exchanges must continue. The potential consequences of COVID-19 outbreaks to human life and to trade necessitate a balanced response. The principles described can offer health, financial, operational, and safety advantages.

Delusions of Certainty: Commercial Vessel COVID-19 Risk Stratification.

Since the World Health Organization's (WHO's) pandemic declaration on March 11, 2020, coronavirus disease 2019 (COVID-19) outbreaks have occurred on numerous maritime vessels and the containment measures, travel restrictions, and border closures continue to make it increasingly difficult for ship operators world-wide to be granted pratique, conduct trade, and conduct crew changes.Knowledge of Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) circulating on-board a ship prior to its arrival has significant implications for the protection of shore-based maritime workers (ie, pilots, stevedores, and surveyors), the broader community, and trade. A useful approach is a graded assessment of the public health risk. The Western Australia (WA) experience and associated observed pitfalls in implementing the prediction equation for the potential presence of SARS-CoV-2 on-board based on five COVID-19 outbreaks on commercial and cruise vessels during 2020 is described.Despite best efforts, the qualitative and quantitative predictors of SARS-CoV-2 circulating on-board commercial vessels are failing to deliver the required certainty, and to date, the only accepted method of ascertaining the presence of SARS-CoV-2 remains the real-time reverse transcription polymerase chain reaction (rRT-PCR) testing reported by an accredited laboratory.Based on legal or regulatory requirements, germane processes, underpinned by robust and auditable processes and procedures, must be put in place to inform the risk assessment of SARS-CoV-2 circulating on-board vessels.

Successful Control of an Onboard COVID-19 Outbreak Using the Cruise Ship as a Quarantine Facility, Western Australia, Australia.

Onboard quarantining has been only partially effective to control outbreaks of coronavirus disease on cruise ships. We describe the successful use of the ship as a quarantine facility during the response to the outbreak on the MS Artania, which docked in Western Australia, Australia. The health-led 14-day quarantine regime was based on established principles of outbreak management and experiences of coronavirus disease outbreaks on cruise ships elsewhere. The attack rate in the crew was 3.3% (28/832) before quarantine commencement and 4.8% (21/441) during quarantine on board. No crew members became symptomatic after completion of quarantine. Infection surveillance involved telephone correspondence, face-to-face visits, and testing for severe acute respiratory syndrome coronavirus 2. No serious health issues were reported, no response staff became infected, and only 1 quarantine breach occurred among crew. Onboard quarantine could offer financial and operational advantages in outbreak response and provide reassurance to the shore-based wider community regarding risk for infection.