Roger-Luc Chayer (Image : AI / Gay Globe)
Alert in Montreal: Shigellosis and Giardiasis Spreading
This morning, I was informed by a reader that he had contracted a disease called shigellosis during an event held at a business in the gay community in Montreal, where a large number of people are allowed to have sexual contact once a month.
He was notified by a Montreal public health nurse following a hospitalization. While reviewing the documentation necessary to prepare this article, I discovered that a shigellosis alert is currently underway in Montreal and primarily affecting the gay community.
The same is true for giardiasis, another infection currently spreading within the gay community, following transmission patterns similar to those of shigellosis.
Let’s discuss.
Shigellosis is an acute intestinal infection caused by bacteria of the genus Shigella. Still largely unknown to the general public, this disease is one of the most common causes of bacterial diarrhea worldwide. Highly contagious, it can spread rapidly in environments with poor hygiene, as well as through close personal contact, including in certain sexual contexts. In Canada, as elsewhere in North America, outbreaks are regularly reported, particularly in urban settings.
A Highly Transmissible Bacterium
Shigellosis is transmitted via the fecal-oral route. In practice, this means infection occurs when a person accidentally ingests bacteria present in contaminated fecal matter. This can happen through contaminated water or food, unwashed hands, or direct close contact.
One of the most concerning aspects of shigellosis is the very low infectious dose required to become ill. Unlike other intestinal bacteria, just a few dozen germs can trigger infection. This explains why the disease spreads easily in daycare centers, shelters, healthcare facilities, or among homeless populations. Outbreaks have also been observed within certain urban communities, particularly among men who have sex with men.
The main species responsible are Shigella sonnei, the most widespread in North America, Shigella flexneri, Shigella dysenteriae, and Shigella boydii. Some strains produce toxins that worsen intestinal inflammation.
Symptoms: Acute Diarrhea and Possible Complications
Symptoms generally appear one to three days after exposure. The most common manifestation is acute diarrhea, sometimes watery, sometimes bloody. It is often accompanied by severe abdominal cramps, fever, nausea, and an urgent, painful need to defecate.
In most cases, the illness lasts five to seven days and resolves spontaneously. However, some individuals may experience significant dehydration, especially young children, the elderly, or those with weakened immune systems. In rare cases, complications can occur, including seizures in children or severe inflammation of the colon.
Some infected individuals may exhibit only mild symptoms or none at all, while still remaining contagious.
Diagnosis and Treatment: Antibiotic Resistance Challenge
Diagnosis of shigellosis relies on laboratory analysis of stool samples to identify the causative bacterium. This step is crucial, particularly to determine antibiotic susceptibility.
In mild cases, treatment primarily focuses on maintaining adequate hydration and monitoring symptom progression. Anti-diarrheal medications are generally discouraged as they may slow bacterial clearance.
In more severe cases, or among individuals at risk of complications, antibiotics may be prescribed to shorten the duration of illness and contagion. A growing concern for health authorities is the rise of antibiotic-resistant strains. Some Shigella forms now show resistance to multiple commonly used treatments, complicating management and sometimes requiring more specific medications.
Giardiasis: Increasing Parasitic Intestinal Infection
Giardiasis is an intestinal infection caused by a microscopic parasite called Giardia lamblia, also known as Giardia intestinalis. It is one of the most common causes of parasitic diarrhea worldwide, including in Canada. Although generally mild, giardiasis can cause persistent symptoms and significantly affect quality of life.
Transmission of Giardiasis
Giardiasis is primarily transmitted via the fecal-oral route. Infection occurs when a person ingests parasite cysts present in water, food, or contaminated surfaces.
Contaminated drinking water or surface water (lakes, rivers) is a frequent source of infection. The parasite is resistant to low concentrations of chlorine, explaining why some outbreaks are linked to poorly treated water networks or freshwater swimming.
Transmission can also occur through direct person-to-person contact, particularly in daycare centers, households, homeless settings, or sexual practices involving oro-anal contact. Very small amounts of the parasite can trigger infection.
Symptoms of Giardiasis
Symptoms usually appear one to two weeks after exposure. Some individuals remain asymptomatic but can still transmit the infection.
When symptoms occur, they include watery or greasy diarrhea, bloating and excessive gas, abdominal cramps, nausea, fatigue, and weight loss. A typical characteristic of giardiasis is foul-smelling, sometimes greasy diarrhea, related to poor nutrient absorption in the intestine. Symptoms can last several weeks or become intermittent. In children, prolonged infection may cause growth delays due to chronic malabsorption.
Diagnosis and Treatment
Diagnosis relies on stool sample analysis to detect the parasite or its antigens. Multiple samples may be necessary, as parasite excretion can be intermittent.
Giardiasis is effectively treated with prescribed antiparasitic medications, such as metronidazole or equivalent drugs. Treatment usually resolves symptoms quickly, although fatigue or digestive issues may persist temporarily.
It is recommended to avoid preparing food and limit close contact while symptomatic to reduce transmission.
Prevention: Simple but Crucial Measures
Prevention of giardiasis depends on strict hygiene measures. Frequent handwashing with soap and water is essential, especially after using the toilet and before handling food.
During hiking or nature trips, boiling water or using appropriate filters is advised before consumption. In urban settings, vigilance is necessary during boil-water advisories or reported outbreaks.
In sexual contexts with fecal exposure risk, using protective barriers and maintaining careful hygiene helps reduce infection risks.
An Infection Not to Be Underestimated
Although rarely severe, giardiasis can become debilitating when prolonged. Its high transmissibility highlights the importance of basic hygiene, even where healthcare and potable water access are adequate.
Better public awareness and prompt consultation in cases of persistent diarrhea help limit spread and prevent unnecessary complications.
Why Is There Currently an Outbreak of Giardiasis and Shigellosis Among Gay Men in Montreal?
Contrary to popular belief, giardiasis and shigellosis are not classic sexually transmitted infections, but they can be transmitted during sexual contact involving fecal or oro-anal exposure. This has been observed in several regions of Canada, including British Columbia, indicating that enteric infections can sometimes spread sexually among men who have sex with men (MSM) through such intimate contact.
High-Risk Contact Modes
Shigellosis and giardiasis spread when fecal cysts or bacteria from one person’s stool are transferred to another’s mouth. This can occur through oro-anal contact, contact with contaminated fingers or sex toys, or poor hand hygiene after anal contact. These well-documented transmission modes facilitate faster spread in contexts where such practices are frequent.
Behavioral Factors
In some sexual networks or community social events involving multiple intimate contacts, enteric infections circulate more easily. Contributing factors include multiple partners in a short period, frequent anal contacts without protective barriers, and reduced precautions against other infections (e.g., increased PrEP use reducing consistent barrier use). Behavioral analyses suggest these factors can alter risk perception and contribute to non-HIV pathogen circulation.
Precedents and Surveillance
Epidemiological studies have shown that, outside of travel-related cases, the proportion of shigellosis among MSM is significantly higher than in the general population due to these transmission modes and the bacterium’s high contagion.
No Stigmatization: An Explainable Phenomenon
These outbreaks are not caused by sexual orientation itself, but by transmission modes associated with specific practices concentrated within certain social networks. Anyone with similar physical contacts or exposure to the same factors can be affected, regardless of orientation.
Transmission and Epidemiological Surveillance in Montreal
The Montreal Regional Public Health Department (DRSP) indicates that Shigella infections circulate regularly in the population, but sexual transmission among MSM has been identified as a risk group in several outbreaks over the years. This means some cases are linked to close contact with fecal or oro-anal exposure.
Although 2026 data may not always be published in real-time, Montreal has historically seen shigellosis outbreaks primarily among MSM, highlighting the role of contact patterns in transmission. Surveillance also indicates rising multidrug-resistant Shigella strains, persisting for several years locally, often linked to sexual or local transmission rather than travel or food.
Why the MSM Community Is Affected
Transmission-prone contact modes: Shigella spreads via fecal-oral routes, but sexual practices involving direct or indirect contact with feces—such as oro-anal contact, sex toys, or manual contact post-anal—can facilitate spread. These modes are not group-specific but explain why the bacteria circulate more easily in sexual networks with these contacts.
Multiple partners and connected sexual networks: In some social and dating networks, close contact with multiple partners, particularly during community events, accelerates pathogen spread.
Limited awareness and prevention for these specific infections: Historically, awareness of enteric infections like shigellosis and giardiasis in sexual contexts has been lower than for classic STIs (e.g., chlamydia, syphilis), limiting adoption of tailored preventive measures.
And Giardiasis?
Quebec epidemiological data show this intestinal parasite is endemic, with seasonal peaks in the general population linked to cyst ingestion via water or contaminated surfaces. Among some gay men, it can also be linked to sexual practices involving fecal-oral contact, though scientific literature notes sexual transmission among MSM is less documented and possibly less frequent than for Shigella.
Why Now in Montreal?
Even if public health documents do not always provide real-time figures, several factors contribute to more frequent enteric infections in certain networks: persistent resistant or locally active strains, social and sexual activity in community settings, and lower awareness of non-foodborne transmission modes among at-risk individuals.
Public Health Recommendations
Although no specific 2026 DRSP statement was found, general recommendations to reduce transmission in these contexts often include strict hand hygiene, limiting fecal-oral contact, using barriers (such as dental dams or adapted condoms), and avoiding sexual contact when gastrointestinal symptoms are present until full resolution.
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