Prashant Kumar’s study on indoor air quality aboard cruise ships highlights the critical role of ventilation and masking in reducing infection risks.
The Caribbean cruise season typically runs from late fall to spring, while the UK/EU cruise season spans from late spring to early fall, bringing millions of passengers aboard ships each year. While cruising provides a unique travel experience, maintaining indoor air quality (IAQ) and preventing the spread of infections remain key concerns for operators. A recent study conducted on a UK and EU cruise ship assessed IAQ and ventilation across various passenger areas, including cabins, dining spaces, and entertainment areas. As part of the EU HEALTHY SAILING project, the study measured CO2 concentrations, temperature, and relative humidity (RH) to evaluate ventilation effectiveness and the potential risk of airborne disease transmission.1
The results showed that CO2 levels in most areas were acceptable, but dining areas like the pub and restaurant recorded CO2 levels above 2000 ppm. These elevated levels, combined with insufficient air exchange, suggest a higher risk of airborne disease transmission. The study emphasizes the need for improved ventilation in these areas.1
In an email interview with Contagion, professor Prashant Kumar, co-director of the Institute for Sustainability at the University of Surrey, UK, discussed specific measures that cruise operators could adopt to mitigate the potential risks associated with high CO2 levels, particularly in the pub and restaurant.
Kumar explained what cruise operators should do to reduce the risk of airborne infections in areas with high CO2 levels, “Apart from considering increasing ventilation rates and ventilation system upgrades, some of the more direct/actionable approaches include (i) enhancing the comprehensiveness of the demand control ventilation (DCV) systems/network by implementing additional real-time CO2 monitoring sensors to ensure IAQ data is captured locally and regionally. And in turn, ensure the system accurately adjusts airflow to meet the needs of a space. These could also enable the identification of spatial variation in IAQ and airborne disease transmission risk, and (ii) limit the occupants within the areas or allow interval breaks within the operational/opening hours to allow for subsequent reduction in CO2 concentration.”
Kumar also emphasized the need for operators to balance infection control with energy efficiency, particularly in areas that showed signs of over-ventilation. He added, “To ensure both infection control and energy efficiency are optimised, future works that are necessary, include reassessing the current HVAC operation modes/configurations to ensure ACH is adjusted corresponding to expected daily occupancy variations or peaks. A comprehensive computational fluid dynamics (CFD) model validation to develop a holistic assessment for a diverse range of passenger ship environments would be a useful first step to building the understanding and balance of both of these elements.”
Kumar emphasized the importance of long-term IAQ data collection to inform ventilation guidelines on passenger ships. He explained, “Our work demonstrates data from low-cost sensors is not limited to understanding IAQ and thermal conditions, but also infection risk and energy consumption evaluation. The study illustrates the importance of including measurements of thermal comfort factors and IAQ for ventilation performance studies. There is a need for continuous, long-term measurements of passenger ships with different indoor design conditions/infrastructures, to build a comparative dataset at different sites and seasons of the year. This work demonstrated that suitable ventilation strategies are in place to enable suitable operation for most of the crowded and enclosed spaces aboard, with a low risk of airborne disease transmission. However, a comprehensive understanding of the spatial variation in IAQ and airborne disease transmission risk would benefit.
The study found that high CO2 levels in dining areas, such as the pub and restaurant, increase the risk of airborne disease transmission aboard cruise ships.
Masking was shown to significantly reduce COVID-19 infection risk on cruise ships, with masked passengers having up to 20 times lower risk than those unmasked.
Long-term indoor air quality data collection is crucial for developing comprehensive ventilation strategies and improving disease prevention on cruise ships.
A separate study conducted from July to November 2021 on COVID-19-vaccinated cruise ships found that masking significantly reduced the risk of infection. Among 11 cruise ships, passengers on nine ships with mandatory masking protocols had a 14.58 times lower risk of infection compared to those on two ships without masking requirements. Additionally, masked passengers had a 19.61 times lower infection risk compared to the broader community.2
The research also emphasized the importance of vaccination in reducing infection risk, with nearly 100% of cruise ship passengers vaccinated compared to 66% in the community. Despite the presence of the Delta variant and older demographics aboard, no severe cases or fatalities were reported. This reinforces the importance of nonpharmaceutical measures (NPMs), including masking and high-efficiency filtration, in preventing the spread of respiratory infections.3
In January 2024, Cunard's Queen Victoria experienced a gastrointestinal illness outbreak linked to norovirus. A total of 129 passengers (7.07%) and 25 crew members (2.59%) reported symptoms such as vomiting and diarrhea. In response, Cunard increased cleaning efforts, isolated affected individuals, and encouraged passengers and crew to report illnesses promptly and practice good hand hygiene. The CDC's Vessel Sanitation Program (VSP) monitored the situation remotely, reviewing outbreak response and sanitation procedures.4
In summary, these findings highlight the importance of improving ventilation and implementing effective infection control measures on cruise ships. By adopting real-time IAQ monitoring, optimizing ventilation rates, and reinforcing masking protocols, cruise operators can significantly reduce the risk of airborne infections while enhancing overall energy efficiency.
