• 20 Apr, 2025
• Magazica

When Cold Days Turn Warm: Medical conditions to monitor when spring transitions to summer in Canada

Canadians have long distinguished “flu season” from the relaxed atmosphere which followed Easter. That tidy separation is fading. The national influenza B virus surveillance data shows that respiratory syncytial virus and the four common human coronaviruses remain active until early April after we discontinue using de-icer for windshield washer fluid. Winter pathogens reach their highest levels between January and March according to laboratory data but now decline more gradually after mid-winter which results in sustained emergency room visits through spring break. Virologists say that cool, dry air just above freezing protects viral particles and dries nasal passages while also pointing out that human behavior takes more time to change than calendar dates. During early spring people flock to crowded buses and classrooms which function as perfect mixing bowls for respiratory droplets. The moral is dull but effective: The winter practices of washing hands, wearing masks when having a fever, and staying indoors with a high temperature remain effective until daffodils start to bloom.

The final surge of winter viruses starts to subside while an unseen wave begins to build up above us. Lengthening days propel tree pollen into the atmosphere with both an earlier start and higher concentrations than twentieth century records show. Research shows Canada’s growing season has shifted six days forward since the 1950s and North American pollen levels have risen by 20 percent over the last three decades. Yellow dust heaps attract botanists but cause sneezing fits along with itchy eyes and allergic rhinitis symptoms for about one quarter of Canadians. Asthmatics experience the most intense effects from these conditions. Their inflamed airways react to the same grains that trigger sneezes, and the traffic is now two way: Inflamed airways from pollen make people more susceptible to viruses which combined with common cold reducing bronchial passage sizes turns simple outdoor meals into urgent nighttime inhaler situations. Pollen tracking should be as regular as snowplow updates for patients according to respiratory educators who also recommend indoor washing and dressing changes because pollen attaches to clothing as strongly as burrs.

The intensity of the season becomes clear through the condition of people’s eyes. Windborne allergens trigger allergic conjunctivitis, which causes non-contagious pink eye cases that fill emergency clinics during April and May. The inflammation is miserable yet often misunderstood: The allergic form of pink eye does not transmit to others. Effective treatment involves both aggressive allergen control measures and cool compresses with antihistamine drops only when required. The distinction between contagious and non-contagious pink eye is important because families may wrongfully keep their children from school or daycare based on infection fears. A doctor’s confirmation that air exposure causes the symptoms allows children to resume playing and parents to return to work while keeping classmates safe.

Tree pollen dominates April, but certain viruses also flourish during these same chilly and humid weeks. The tough adenoviruses that show symptoms similar to influenza, through sore throats and persistent coughs, flourish during warm-weather conditions. Viruses can survive for hours on plastic and steel surfaces, making handrails, toys, and cafeteria tables ideal platforms for transmission. The absence of a seasonal vaccine for adenovirus results in soap, ventilation, and home rest remaining as the only dependable methods to combat it, unlike influenza and COVID-19. Effective disease control in schools is possible through regular disinfection of door handles and the practice of quick hand washing after recess.

Life begins to stir in the brown leaf mat from last year when daytime highs exceed the freezing point for extended afternoon periods. The black legged tick stands as the prime example of how climate change is silently altering health risks in Canada. Prolonged winter cold prevented the species from advancing north as it remained south of the border two decades earlier. Current research indicates that climate change has pushed both the black-legged tick and its Lyme disease bacterium progressively northward to create risk areas beginning in southern Ontario, followed by Quebec, and eventually the Maritimes. Ticks can become active during brief periods above freezing temperatures, which means people need to perform “tick checks” as early as April and late March instead of just during midsummer hikes. Hikers who enjoy spending time outdoors should wear light-colored pants, which make it easier to spot dark specks moving up their legs while also tucking pant cuffs into socks and checking their skin behind knees and near the hairline after walking through brushy areas or wet meadows. The early administration of antibiotics eliminates most long-term damage when a tick bite leads to the appearance of a bull’s eye rash at the bite site. By waiting too long before taking action, patients risk developing fever and joint pain and may experience neurological problems in uncommon situations. The disease burden has dramatically decreased because patients in the Québec City corridor are seeking treatment at earlier stages as public awareness rises, according to local physicians.

Ticks share the benefit of extended Canadian summer seasons with other creatures. Mosquito season expands earlier because mild spring temperatures lengthen their breeding period. The appearance of West Nile virus in surveillance traps throughout the Prairies and southern Ontario now begins as early as June, which defies its former classification as a late August threat. Predictive models indicate that by the 2080s, Culex tarsalis—the Prairie mosquito that most effectively transmits the virus—will remain infectious for five months during warmer evenings instead of three, while Culex pipiens will spread further into cottage country. Public health agencies recommend using repellent sooner, along with installing window screens earlier and checking backyard drains earlier, due to warmer weather starting earlier. The biggest risk nests in familiar places: Eavestroughs blocked by fallen leaves, combined with neglected bird baths and rain-filled inverted covers, create ideal mosquito breeding grounds. Every location functions as a production center that generates hundreds of mosquitoes. Targeting mosquito breeding sites in May cuts down on the summer buzzing pain in July.

The viruses that attack during recreational water season target pools, splash pads, and shallow lakes along this aquatic line. Enteroviruses appear at the top of the list because they cause hand, foot, and mouth disease in young children. Warm stagnant water provides ideal growing conditions for these organisms, which then spread through microscopic stool particles according to scientific facts, not poetic imagery. Enteroviruses spread when toddlers wearing swim diapers share a wading pool or when campers use the same water to clean dishes that they drink from. Public beaches require families to adopt preventative measures like college camps and day care programs that position soap dispensers outside latrines. The cruise ship menace known as Norovirus thrives during warm months since people consume picnic foods that multiple individuals handle. Old-fashioned soap and water remain the best option because they survive common alcohol based hand gels and require twenty seconds of scrubbing even when the lake calls.

The distinctive aroma of recent spring seasons comes from distant wood smoke fires, while bird song and bicycle bells create the auditory backdrop. The unprecedented 2023 Canadian wildfire season left urban skies across Vancouver and Halifax darkened and taught people that air quality can degrade swiftly, even with long-standing industrial emission regulations. When boreal forests burn, they release fine particles that irritate airways and inflame lung tissue while entering the bloodstream to worsen heart conditions. Doctors who treated children with respiratory problems in smoky cities observed measurable lung function declines that remained weeks after the smog lifted. Smoke alters spring’s respiratory landscape in two ways: Smoke exposure leads to instant asthma attacks and reduces the resistance of healthy lungs to airborne viruses and pollens. Residents should now monitor the Air Quality Health Index first thing in the morning like they used to check wind chill before starting their day. People can reduce particle exposure during high smoke days by staying indoors for exercise and using HEPA filters or HVAC systems at home while wearing properly fitting N 95 masks when outside. Masks originally used for protecting against viruses function just as effectively at filtering smoke particles.

The midpoint starts to change again when the days of June extend into July. Once tree pollen decreases its presence, grass pollen emerges dominantly which leads to a challenging period for people allergic to both pollen types known as the “double whammy” season. The immune system is not prepared to handle extended inhalation of irritating proteins which leads to gritty eyes and raw throats that persist throughout patio dining season. The mosquito-transmitted heartworm parasite which affects dogs and sometimes cats thrives when temperatures rise above 14 °C. In hot regions veterinarians now extend preventive medication treatments from six months to eight or ten months.

As temperatures rise during summer seasons buildings cooling systems become silent hosts for Legionella bacteria growth. Poorly maintained cooling towers can become breeding grounds for Legionnaires’ disease bacteria when outside air temperatures rise. Breathing in mist from contaminated water sources such as decorative fountains and rooftop air conditioning systems can result in severe pneumonia. Investigators search for bacterial sources in large buildings that failed to maintain regular cleaning or chlorination throughout pandemic periods. COVID 19 disrupted maintenance schedules which are now being reconstructed with climate considerations to enable shorter maintenance intervals and mid-season inspections.

Against this catalogue of irritants, microbes and parasites, it is worth recalling that nature also delivers springtime euphoria: Additional daylight enhances mood while moderate exercise reduces blood pressure and fresh produce provides abundant vitamins meanwhile brief interaction with green spaces helps reduce mental exhaustion. Our outdoor passion faces threats not from nature itself but from a few avoidable dangers that accompany us during nice weather. The same science that maps a new tick habitat also maps the simplest defence: long socks, thorough checks, and prompt removal. Research predicting extended allergy seasons shows that washing hair and changing clothes reduces indoor allergens by 50%. Preventive health practices become routine rather than burdensome when we view them as simple daily rituals like applying sunblock or carrying an inhaler.

Climate change operates as the hidden force behind numerous changes yet it doesn’t serve as a harbinger of catastrophe or a justification for hopelessness.

References

Asthma Canada. (n.d.). Spring weather brings the promise of more opportunities to spend time outdoors. https://asthma.ca

Dangerfield, K. (2024, May 1). As flu season fades, spring and summer viruses emerge. What are they? Global News. https://globalnews.ca

Heid, M. (2018, March 19). Are you more likely to get sick when the seasons change? Here’s what experts say. TIME. https://time.com

Jarry, J. (2020, July 24). A virus for every season. McGill Office for Science & Society. https://mcgill.ca/oss

Lagacé-Wiens, P., Bullard, J., Cole, R., & Van Caeseele, P. (2021). Seasonality of coronaviruses and other respiratory viruses in Canada: Implications for COVID-19. Canada Communicable Disease Report, 47(3), 132–138. https://doi.org/10.14745/ccdr.v47i03a02

Nandi, P. (2023, April 10). Here’s what you can do to beat these common springtime illnesses. WXYZ-TV News. https://wxyz.com

Ogden, N. H., Bouchard, C., Brankston, G., Brown, E. M., Corrin, T., Drebot, M. A., … Wood, H. (2022). Infectious diseases (Chapter 6). In P. Berry & R. Schnitter (Eds.), Health of Canadians in a changing climate: Advancing our knowledge for action (pp. 367–443). Government of Canada. https://changingclimate.ca

Omstead, J. (2025, March 22). The five senses of spring: How climate change is shaping our seasonal experience. The Canadian Press. https://globalnews.ca

Teladoc Health. (n.d.). It’s finally spring! Not just on the calendar, but in the air. https://teladochealth.com