In her job as a physician at the Boston Medical Center in Massachusetts, Sondra Crosby treated some of the first people in her region to get COVID-19. So when she began feeling sick in April, Crosby wasn’t surprised to learn that she, too, had been infected. At first, her symptoms felt like those of a bad cold, but by the next day, she was too sick to get out of bed. She struggled to eat and depended on her husband to bring her sports drinks and fever-reducing medicine. Then she lost track of time completely.

For five days, Crosby lay in a confused haze, unable to remember the simplest things, such as how to turn on her phone or what her address was. She began hallucinating, seeing lizards on her walls and smelling a repugnant reptilian odour. Only later did Crosby realize that she had had delirium, the formal medical term for her abrupt, severe disorientation.

Delirium is so common in COVID-19 that some researchers have proposed making the condition one of the disease’s diagnostic criteria. The pandemic has sparked physicians’ interest in the condition, says Sharon Inouye, a geriatrician at the Marcus Institute for Aging and Harvard Medical School in Boston, who has studied delirium for more than 30 years.

If the pandemic can be said to have a silver lining, says Inouye, it has been to spur interest in how delirium can lead to dementia — and vice versa. What’s more, says Catherine Price, a neuropsychologist at the University of Florida in Gainesville, the spread of COVID-19 “has highlighted the blurring of the lines between delirium and dementia, especially with more older adults in our populace”.

The high numbers of people who developed delirium immediately made Inouye, Price and other researchers worry that the pandemic could lead to a surge in dementia cases in the coming decades, on top of the increase in cases as a result of ageing populations (see ‘The cost of delirium’). “Is there going to be an increase in dementia from people who had COVID-19 during adulthood or midlife?” asks Natalie Tronson, a neuropsychologist at the University of Michigan in Ann Arbor. “What happens over the next decades, as the population ages more?”

Read the full article at Nature.