Car sharing has been identified by NHS Western Isles as a factor in the spread of Covid-19 in Uist.
Mild symptoms have also been identified as causing delays in people getting tested and self-isolating, allowing the outbreak to spread.
The health board has told people to avoid car-sharing with anyone from outside their household, and issued detailed guidelines for those who can’t avoid it, including those taking driving lessons.
The precautions include limiting the number of people in the vehicle, washing hands before entering and after leaving the vehicle, maintaining good ventilation and opening windows for the duration of the journey.
Car sharers are also advised to sit as far apart as possible and wear a face mask or covering for the duration of the journey.
Door handles and any other surfaces people touch in the car should be wiped down before and after the journey.
The health board says if there is no alternative but to car share, steps should be taken to share with the same individuals each time.
An NHS Western Isles spokeswoman said: “We have become aware through the contact tracing process that spread of Covid-19 in Uist can happen as a result of car sharing outwith households.
“Covid-19 spreads quickly and easily in cars, even when people are wearing masks.”
A feature of the current outbreak in South Uist, Eriskay and Benbecula is that the vast majority of people who have contracted Covid-19 have experienced mild symptoms.
The spokeswoman said: “Whilst this is clearly something that is positive for those individuals affected, it also means that they have been later in self isolating and requesting a test, which did result in further spread to close contacts.
“If you are experiencing any symptoms of Covid-19, no matter how mild, please self-isolate and book a test immediately to help prevent any further spread.
“You should continue to self-isolate until you have been told the outcome of your COVID-19 test.”
Information about how to self-isolate and support on offer is available at coronavirus.wi.nhs.scot
The total number of cases on the islands since the start of the pandemic is 56, with no recorded loss of life, according to NHS Western Isles.
There have been 48 cases in South Uist, one in North Uist, and seven on Lewis.
National figures show a total of 58 cases but NHS Western Isles re-tested two of those and said they were false positives.
The health board has also reminded communities across the Western Isles that physical distancing, hand and respiratory hygiene, the use of face masks and coverings, and not entering other households or have others entering your home are all vitally important to prevent further spread of Covid-19.