Many of the patients taken ill across Scotland are suffering from a particularly serious strain of flu believed to have originated in Australia.
What has commonly been called “Aussie flu” is technically termed H3N2, and it was blamed for the deaths of 300 people in Australia during their winter.
One in four cases of flu being handled in the UK are thought to be patients battling the “Aussie strain”.
Its symptoms are worse than other forms of the virus, with more severe instances of coughing, exhaustion, fever, headaches, sore throats and vomiting being reported.
Doctors have stressed that a flu jab is the best way to combat the bug, and began offering free jabs to certain patient groups in October.
Vulnerable groups include people aged 65 or older, pregnant women and anyone with a long-term medical condition such as diabetes or a heart, lung, kidney or neurological disease.
Slightly more than half of the circulating strains of flu match those in the 2017/18 vaccine, including the H3N2 strain.
Catherine Stokoe, head of infection control in NHS Highland, offered advice to help keep people safe during the outbreak.
She said: “People suffering with flu-like symptoms should cough or sneeze into tissues and bin them immediately, wash their hands regularly with soap and warm water and frequently clean regularly used surfaces to stop the spread of flu.”
Experts at NHS Grampian have also been encouraged by the growing number of medics who have taken care to immunise themselves this winter.
People can contact their local GP practice to arrange an appointment to be vaccinated, or can call the NHS on 0800 22 44 88 for more information.