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COVID-19 tests may give false sense of security

While access to coronavirus testing for seafarers is now becoming more widely available, ship operators should bear in mind that no test is 100% accurate. As explained by Dr. Ingrid H. Johansen, a two-week quarantine for on-signing crew at the place of embarkation should still be the primary measure to prevent infected seafarers from joining a ship.

The IMO, together with a number of industry organisations, have put together a recommended framework of protocols for ensuring safe ship crew changes and travel during the coronavirus (COVID-19) pandemic (IMO MSC.1/Circ.1636). These protocols provide recommendations to ship operators and seafarers, governments, maritime administrations, port authorities and all other stakeholders involved in crew changes on how to manage and control the risk of seafarers becoming infected prior to leaving home, while travelling to join a ship and during repatriation.

At a time when many ports and countries operate with differing COVID-19 regulations, it is important for ship operators to build trust and confidence with the authorities. Ship operators are therefore encouraged to implement all relevant recommendations set out in the IMO protocols, and include measures such as seafarers’ self-monitoring of their own health, the proper use of Personal Protection Equipment (PPE), adherence to social distancing and application of an efficient combination of quarantine and testing, if suitable test kits are available. Implementation of the protocols should also be supported by documentation in order to facilitate recognition of adherence to these recommendations throughout the crew change and travel process.

Gard’s recent experience

Despite ship operators’ and seafarers' best efforts to ensure safe crew changes, we are seeing an increase in the number of cases where relieving crewmembers are infected with COVID-19. We also see that ship operators increasingly rely on testing of seafarers as part of their crew change policy.

In our Insight “An introduction to testing for COVID-19” of 2 June 2020, Dr. Ingrid H. Johansen at the Norwegian Centre for Maritime and Diving Medicine explains the complexity of testing for COVID-19. In this follow-up article, she explains why ship operators need to combine testing with the use of quarantine to ensure safe crew changes.

We are grateful to Ingrid H. Johansen for sharing the following interesting and useful insight on this topic:


The problem of negative COVID-19 tests

The test method currently recommended for detecting the novel coronavirus is known as Polymerase Chain Reaction, or PCR-testing. As explained in Gard's previous Insight, while PCR-tests are considered to accurately identify genetic material from viruses, there are inherent problems when relying on such tests. Most importantly, users must be aware that a PCR-test result:

  • is only a snapshot of the level of virus in the body at the point in time when the test was taken;
  • says nothing about what will happen in the days after the test was taken;
  • will not detect whether the subject has had COVID-19 in the past; and
  • can, if taken too soon after infection, show a ‘false negative’ as the levels of virus in the body are still too low to be detected.

In addition, all tests, test procedures and analyses carry some uncertainty. The test methods may not be accurate or specific enough. The test samples may not be good enough, or there may be problems in the analysis of the tests, such as contamination by other tests. Hence, even if the PCR-tests are considered to be accurate and the risk of experiencing ‘false positives’ is very low, the risk of ‘false negatives’ cannot be ruled out. The Gard case reported below demonstrates how relying on test results alone can be a risky approach.


Case example no.1  

A young and healthy seafarer took two PCR-tests three days apart before travelling from his home country and joined the ship four days after his last negative test. The following day he fell ill with a high fever. He was immediately isolated in the ship’s sickbay, and all necessary precautions were taken to prevent the spread of a potential communicable disease. The day after falling ill he was brought ashore for a medical examination and tested positive for COVID-19. A total of six days had passed between the seafarer’s last negative and first positive test for COVID-19.


As the above case example shows, PCR-tests cannot fully replace quarantine when conducting crew changes. Testing must always be used in combination with quarantine and other behavioural measures, such as use of PPE and social distancing, in order to properly manage and control the risks of seafarers becoming infected.  

The crucial COVID-19 timelines

Why is the timing of testing essential? As explained in Gard's previous Insight, the PCR-test looks for an active virus in the body. For a virus to be active, it must have started spreading in the body. We know that PCR-testing is most likely to find the virus between day 3 and day 8 following infection, which means that if the test is taken too early after a person has been infected, the virus might not be detected.

How long does it take for symptoms to appear? On average it takes 5-6 days from infection until symptoms show and almost everybody who develop symptoms do so within 14 days from infection. Among these, 50% will fall ill in the first five days after infection and as many as 97.5% will have fallen ill by day 12. Most people start with mild symptoms and those who develop severe illness, normally do so approximately one week after the first symptoms appeared. We also know that there is a subset of people who are infected that never develop noticeable symptoms, but at the time of writing we do not know the proportion who fall into this category.

When is the disease most contagious? People infected by the virus are most contagious in the early stages. Among those who fall ill, we know that the risk of transmitting the disease to others is highest in the 48 hours before they show symptoms. The risk of transmitting the disease starts to decline 7 days after the first symptoms appeared, and it is considered unlikely that transmission occurs more than 10 days after a person became symptomatic. Infected people with no symptoms can still transmit the virus to others, but we do not currently know how often it happens.

Reverting to Gard's Case example no.1, it is impossible to know whether the young seafarer was infected with the virus before the second test was taken in his home country or during his journey to the ship or whether the PCR-tests were accurate or not. What is evident is that he posed a substantial risk to the rest of the crew from the moment he signed on. The best way to prevent this situation from happening would have been to quarantine him for a sufficient period of time between arrival at port and before joining the ship.

Always use tests in collaboration with qualified health personnel

Another recent case reported to Gard demonstrates how complex testing for COVID-19 might be.


Case example no.2 

A group of seafarers travelled from their home country and arrived at the place of joining the ship two days later. All the seafarers carried proof of negative PCR-tests taken immediately before leaving their home country and they were equipped with hand sanitizers, face masks and gloves before travelling. The day after arrival at the place of embarkation, repeat PCR-tests were taken. When the results were received two days later, the entire group of seafarers had tested positive for COVID-19 and they were all placed in quarantine for seven days in accordance with local regulations. After completing their quarantine period, approximately ten days after their first positive test, the seafarers were re-tested. The results showed that one seafarer still tested positive for COVID-19 while the others tested negative. How can this be explained?


Let us assume for case example no.2 that there were no problems with the test procedures or false test certificates. Most likely the seafarers were infected by the virus just before the tests were taken in their home country, or alternatively during their journey. Their bodies successfully overcame the virus, and the virus could therefore not be detected in the third round of testing. The seafarer who still tested positive could have what is called ‘prolonged virus shedding’, a rare condition in which the virus can be found in tests long after initial infection and resolution of any symptoms. Although we can never be 100% certain, evidence to date suggests that a person with prolonged virus shedding is not a transmission risk to others.  

Despite the possible explanation for the results in Gard's Case example no.2, the case also demonstrates that interpreting test results can be challenging and highlights how important it is to carry out testing in close collaboration with qualified health personnel.

Recommended combinations of testing and quarantine

Some countries who supply seafarers to the global fleet require testing as a prerequisite for travel. Testing and quarantine in a seafarer’s home country can prevent seafarers travelling to and joining the ship while infected, and it prevents the risk of transmission to others during travel. However, as discussed in our case examples above, there is still a risk that seafarers can be infected just before or while travelling from their home country to the port. Since we know that PCR-tests are most likely to detect the virus 3 to 8 days after infection, a best practice in order to prevent infected seafarers from joining ships will therefore be to combine testing in a seafarer’s home country with sufficient time in quarantine and additional testing at a place close to the port.

In July 2020, the International Maritime Health Association (IMHA) published a statement on “Getting healthy seafarers to a ship: Mitigating the risk with quarantine and testing” and their experts provide the following “gold standard guidance” on how to best combine testing and quarantine as part of a crew change policy:


The aim of the first test is to stop ill seafarers from travelling. The aim of the second test is to detect infection with the virus just before and during the journey. The aim of the third test is to clear the person completely before joining the ship. The IMHA statement also provides advice on how best to carry out the quarantine.

While we are aware that implementation of the above procedures may be challenging in some geographical locations, and that local authorities may have their own set of requirements, we encourage ship operators to carefully evaluate their crew change policy in light of the above. Remember, it is important to always weigh any practical and cost implications of implementing these measures against the potential consequences of introducing the coronavirus onboard a ship.

Will an increase in immunity ease the situation?

We will gradually move towards a situation where more and more seafarers have been infected with the virus. Some of the seafarers have recovered from the disease, while many will be unaware that they have ever been infected. These seafarers may be immune to the disease in the future. However, because the virus has only been around for a limited time, this remains to be confirmed. In addition, we do not know for certain how long the immunity will last, or if the virus itself will gradually change and be able to re-infect people. At the time of writing, health authorities are therefore hesitant about declaring a specific period of immunity for people who have recovered from a COVID-19 infection.

We can hope that sometime in the future, the safest approach to keeping a ship free of COVID-19 will shift from using pre-boarding quarantines and testing, to signing on seafarers who have been declared immune - or alternatively - vaccinated.


Gard's summary and recommendations

Arranging crew changes is one of the biggest challenges and ‘safety dilemmas’ the shipping industry is currently facing. On the one hand, due to COVID-19 restrictions, large numbers of seafarers have had their contracts extended, unable to be relieved by a crew change after a long tour of duty. This situation is clearly unsustainable and severely affects the wellbeing and safety of seafarers and the safe operation of ships. On the other hand, crew changes can also increase the likelihood of introducing the novel coronavirus onboard ships.

In order to facilitate the safe rotation of seafarers as well as help protect the health of the general public during the COVID-19 pandemic, the global shipping industry and national governments must adopt the crew change protocols set out in IMO MSC.1/Circ.1636 and other health guidances such as:

With access to COVID-19 testing for seafarers becoming more widely available, we recommend that ship operators carefully consider how to best combine testing with time in quarantine as part of their crew change policy. As explained by Dr. Ingrid H. Johansen, no test is 100% accurate and the use of tests alone should never replace quarantines. She also underlines that caution must be exercised if tests are being used to shorten the quarantine time and warns that this may substantially increase the risk of introducing the coronavirus onboard. Until we know more about how long a person who has recovered from COVID-19 will be safe from reinfection, implementation of pre-boarding quarantines at the place of embarkation - with or without testing - should be regarded as the primary measure to prevent infected seafarers from joining a ship.




Looking for additional sources of information on COVID-19? Please go to Gard’s COVID-19 hot-topic page for a compilation of links to relevant websites, guidelines, and Gard material that may assist ship operators, masters and crews to stay alert and prepare and respond to the COVID-19 outbreak.

  • Ingrid H. Johansen, MD, PhD

    By Ingrid H. Johansen, MD, PhD

    Senior Consultant at the Norwegian Centre for Maritime and Diving Medicine

  • Kristin Urdahl

    By Kristin Urdahl

    Senior Loss Prevention Executive, Arendal

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