Three Canadian provinces are recording more cases than usual of a potentially fatal bacterial infection, prompting Toronto to issue a warning for people travelling to or from Saudi Arabia, and compelling Manitoba and Quebec to change their vaccination policies.

Since January, Toronto has reported 14 cases of invasive meningococcal disease, a rare infection that can lead to meningitis, blood infections and other severe complications. Toronto normally sees six cases of IMD per year.

All 14 patients were admitted to hospital, and two died, including a child, according to Vinita Dubey, Toronto’s associate medical officer of health.

IMD “is really one of those scary diseases because someone can be really healthy, vibrant, carrying on with their life and then get very, very sick very, very quickly,” Dr. Dubey said.

It’s not clear what’s behind the increase in IMD in Ontario, Manitoba and Quebec. Most of the stricken patients weren’t linked to each other through known contacts, and the bacteria that made them sick were sometimes from different serogroups, meaning they couldn’t have come from a common source.

Other parts of Canada haven’t reported similar increases, according to the Public Health Agency of Canada and a Globe and Mail survey of provincial public health officials.

However, in at least six of the Toronto cases, whole genome sequencing of the bacteria revealed it to be a match for a genotype detected in Saudi Arabia. That genotype was also implicated in cases reported in the United States, Britain and France in the spring, all of which were linked to Umrah, an Islamic pilgrimage to Mecca that can take place any time of year.

The strain is a member of serogroup W, which Dr. Dubey said is considered a “hypervirulent” strain.

Despite the matching genetic sequences, the six Toronto patients had not travelled to Saudi Arabia or been in contact with anyone who had travelled. That’s not a total surprise, Dr. Dubey said, considering asymptomatic people can carry the bacteria in the back of their nose or throat and unwittingly spread it through close contact such as kissing or sharing food and utensils.

Toronto Public Health offered antibiotics and vaccines to close contacts of the patients. They are also urging people returning from the annual Hajj pilgrimage to Mecca, which took place June 14-19, to get the meningococcal vaccine and monitor themselves for symptoms, which can include a sudden fever, intense headache, stiff neck, vomiting, dizziness and a rash.

Quebec has recorded 31 cases of IMD since January, most of which were serogroup Y, as well as two IMD-related deaths. Between 2010 and 2019, the province normally saw six cases a year of serogroup Y. The increase in the serogroup dates back to 2022, leading to a change in vaccination policy last year.

In most of Canada, babies receive a shot targeting meningococcal C at 12 months of age, and a quadrivalent shot that protects against serogroups A, Y, C and W in middle school. Quebec, however, used to offer only the meningococcal C vaccine to adolescents. In fall 2023, it began offering the quadrivalent shot to them.

The Kingston, Ont., area reported three non-fatal cases of IMD over the winter: two in late 2023, and one in February of this year. The cases were the first since 2013, said Piotr Oglaza, medical officer of health for Kingston and the surrounding region.

All were serogroup B, but the patients didn’t know each other or share any contacts. The type of bacteria that caused the first two cases, which were discovered close to one another in time, weren’t genetically similar either, Dr. Oglaza said.

“We don’t have a good answer to what might be driving this,” he said, adding that public health officials continue to monitor the situation closely.

Public Health Ontario reported 17 cases province-wide of IMD as of the end of April, more than twice the average of eight cases identified by the same point in the last five years.

In Manitoba, 19 cases have been reported since December, all but one of them part of serogroup W. One adult died. Six cases are typically reported in the province annually.

Most of the Manitoba cases occurred before the Toronto serogroup W cases, and the bacteria that caused them are not genetically similar to the cases emanating from Saudi Arabia.

The unusual spike in Manitoba hit young children hardest, prompting a significant change in vaccination policy, said Carol Kurbis, a medical officer of health for the province.

As of March 1, Manitoba began offering the quadrivalent shot to babies at 12 months as well as to toddlers and preschoolers who had previously received the meningococcal C vaccine.

“We really wanted to move quickly to try to protect infants as much as we could from this current outbreak,” Dr. Kurbis said.