Infectious Diseases

Infectious diseases are illnesses caused by another organism: a virus, a bacterium, a fungus or a parasite. What links them is not the organ they affect but that they can be passed on, and that for many there is a vaccine or a specific treatment. This page is a way in to the individual infections.

Conditions in this area

• COVID-19: still circulating and still behind thousands of deaths a year in Canada, though it looks different now than in 2020.
• Cold and influenza: two different illnesses caused by different viruses. Influenza alone is linked to about 15,000 hospital admissions a year here.
• RSV and RSV vaccination: cold-like illness in most adults, but serious chest infections in babies and older adults.
• Pneumococcal disease and vaccination: a bacterium many people carry harmlessly that sometimes causes pneumonia, blood infection or meningitis.
• Meningococcal disease and vaccination: uncommon but fast-moving, and the reason a fever with a stiff neck is an emergency.
• Lyme disease: a tick-borne infection spreading across Canada, with 5,809 reported cases in 2024.
• Cytomegalovirus (CMV): harmless for most people, but the most common infection passed to a baby before birth.
• Rotavirus: watery diarrhoea and vomiting in babies and young children, with dehydration as the real risk.
• E. coli infection and vaccine research: most strains live harmlessly in the gut, while a few cause serious food and water-borne illness.
• HPV and HPV vaccination: the most common sexually transmitted infection in Canada, linked to several cancers.
• Shingles and post-herpetic neuralgia: the chickenpox virus reactivating decades later, sometimes leaving lasting nerve pain.
• Skin infections: bacteria, fungi and viruses each cause them, and telling them apart changes the treatment.

What these conditions have in common

Every infection here begins with an organism getting somewhere it should not be, and the body’s response is often what you actually feel: fever, aching, tiredness. That is why the same handful of tests keeps appearing, including swabs, blood cultures and stool tests, and why the same questions get asked about who else is affected. Several of these infections are notifiable, meaning cases are reported to public health.

The other thing they share is that most can be reduced, through immunisation, tick and food precautions, or indoor air quality. That sets this group apart, and it explains why so much research here happens in people who are well rather than unwell: vaccine studies are the main way progress is made.

Treatment and management in Canada

Treatment depends on the organism, and getting that right matters more here than in most areas. Care may involve:

• Rest, fluids and treatment of symptoms, all most viral infections need
• Antibiotics for bacterial infections, chosen to limit antibiotic resistance
• Antiviral medicines for some infections, including influenza and COVID-19, usually started early
• Antifungal and antiparasitic medicines where those organisms are involved
• Immunisation, including the childhood schedule, seasonal respiratory vaccines and vaccines offered by age or risk group
• Hospital care, including oxygen and intravenous treatment, in severe infection

What applies to you depends on the infection, your age and your other conditions. Those are decisions for you and your own clinician or pharmacist, and nothing here is a recommendation.

When to talk to a doctor

• Trouble breathing, chest pain, confusion, a rash like small bruises that does not fade when pressed, or a fever with a stiff neck needs emergency care. Call 911 or go to an emergency department.
• A fever in a baby under three months old needs same-day assessment.
• Spreading redness around a wound or bite, with fever, needs same-day assessment.
• Dehydration, including passing very little urine, dizziness on standing or unusual drowsiness, needs same-day assessment.
• Symptoms that improve then clearly worsen again should be reassessed.
• If you have a weakened immune system, contact your care team early rather than waiting.

Why research in this area matters

Some infections here have no vaccine at all. Cytomegalovirus is the most common infection passed to a baby before birth, and there is nothing yet to immunise against it. Lyme disease has no human vaccine in Canada. Others have vaccines whose protection fades, or that need updating as the organism changes, which is why influenza and COVID-19 vaccines are revisited yearly. Antibiotic resistance is pushing research towards new antibacterial agents.

Much of this research needs volunteers who are well, not only people who are unwell. Participation is voluntary, you give informed consent first, and you can withdraw at any time without affecting the care you get from your own doctor. No one can tell in advance whether a study will benefit you personally, and a vaccine study cannot promise protection.

Learn more from Canadian sources

• Public Health Agency of Canada: infectious diseases
• Canadian Immunization Guide
• Provincial and territorial immunization information
• Immunize Canada
• Public Health Agency of Canada: respiratory virus reports