This past week, Paris’ Mayor Anna Hidalgo and other officials swam in the Seine to reassure the Olympic competitors and public that the river is safe and the pollution has been cleaned up. With all the talk of the dangers of swimming in the Seine, it’s a good time to mention other health risks to the throngs of visitors traveling to Paris.
Dengue
Dengue and other arboviral infections are of particular concern. Last September, several people without any history of travel became ill with dengue in Paris. That demonstrated for the first time that dengue can be transmitted locally in northern Europe. Dengue cases are steadily rising globally, from 5.2 million cases in 2016 to almost 10.5 million in the Americas in 2024.
Dengue is transmitted by Aedes albopictus, the tiger mosquito, which feeds on humans. The tiger mosquito is especially problematic because it only requires tiny amounts of water (e.g., a bottlecap) for its eggs, which can withstand being dried out for months. Notably, the dengue virus can be passed down from the mother mozzie through her eggs. When it rains again, the eggs are resurrected and hatch, starting a new breeding and infection cycle.
Many athletes will arrive in France from countries endemic for arboviral infections (dengue, Chikungunya, Zika) and malaria. Almost all malaria cases were imported into France (2,783 in 2022); seven were acquired in the EU.
Covid and influenza
According to the World Health Organization, influenza activity is elevated, with they A(H3N2) virus from South America and the A(H1N1) virus in Africa and Oceania.
Weekly new cases of Covid are high, particularly in the UK, Portugal, and Greece, in Europe and China, Thailand, and New Zealand. SARS-CoV-2 wastewater levels are again rising in much of the U.S. Mike Hoerger, Ph.D., Covid forecaster, notes that current transmission is >3x higher than what is typical for this time of year.
Many Olympic and Tour de France athletes are wearing masks to protect themselves from infection after years of training for the events. For the Belgian team, masking will be compulsory. Five of 176 riders in the Tour dropped out due to Covid infections. Two Swiss Olympic mountain bikers have already withdrawn due to illness, as have British athletes Holly Bradshaw & Sarah McDonald.
The Olympics are expected to draw 15 million visitors, 2 million from outside the region. Given the experience of Taylor Swift’s concerts, which apparently were superspreader events, one might expect an outbreak of Covid to occur in these packed venues. Covid can be transmitted outdoors, too, in crowded conditions.
The Seine Water Quality
The Seine has been off-limits to swimming for more than 100 years due to the river’s pollution levels. Historically, overflow from sewage pipes mixes with excess rainwater and is dumped directly into the river after heavy rains. Massive efforts to clean up the pollution were undertaken, including building a vast rainwater storage facility, holding the equivalent of 20 Olympic-size swimming pools of water. This cost at least ($1.55 billion).
This week, to reassure the public about the safety of the Seine River, Mayor Anna Hidalgo and others took a dip in the river. They felt “safe” doing so, as the E. coli bacteria levels had dropped significantly on Tuesday, following a significant spike the previous Friday due to a major rain event. The levels reported were below the World Triathlon Federation limits of 1000 CFUs/100 ml.
French officials should not be quite so reassured by those counts. Fluidion, a water intelligence company headquartered in Paris and Los Angeles, has been testing the Seine River and providing its data for open access. Fluidion uses a novel technology that is able to provide additional insight into water quality, such as measuring both “free” (or planktonic) E. coli bacterial count and the comprehensive E. coli count, which includes bacteria that are aggregated with stool particles and other sewage.
Dan Angelescu, founder and CEO of Fluidion, explained via email that standard microbiological laboratory methods were designed for waters containing only “free” E. coli bacteria and are therefore blind to E.coli aggregates.
In this graph, you can see that what is more concerning is the “comprehensive” E. coli level. Those levels (the red triangles) are often higher than the thresholds approved by the World Triathlon Federation. The technique used by authorities may seriously underestimate the risk. The red triangles of the “comprehensive” E. coli level could provide a more accurate representation of the actual risk.
Although the weather gods appear to be favoring Paris with high temperatures only in the mid-80s and scant rain during the Olympics, other concerns remain.
Water quality has plagued other Olympics. For example, Brazil’s 2016 Olympics was concerned about “Rio Sewercide” and athletes at risk of multi-drug resistant (CRE) infections from the filthy water.
Leptospirosis remains a concern, as very few bacteria are needed to cause this infection. Any freshwater sports participants are at risk for this infection, transmitted by infected animal urine contaminating the water. Rodents are often the source. Outbreaks have occurred after flooding and a whitewater rafting trip. Symptoms include headache, fever, muscle aches, and redness of the conjunctiva.
Heat Stroke, Air Pollution, And Other Infections
Paris was ranked as the fourth-highest European city with deadly air pollution by Lancet Planetary Health. The influx of tourists will likely worsen this year, causing considerable respiratory distress and illnesses.
The air pollution will also likely exacerbate visitors’ problems with the heat. Officials are warning the public and staff about the possibility of heat stroke. Asthma and COPD also worsen with poor air quality.
Foodborne infections (e.g., Listeria or Salmonella) and GI bugs like norovirus are to be expected.
Whooping cough (pertussis) is having a resurgence in Europe. the European Centre for Disease Prevention and Control recorded 25,130 cases of whooping cough in 2023 compared to 32,037 cases just between January 1 and March 31, 2024. More than 5,800 cases were in France in these three months. This infection, known as the 100-day cough, is transmitted through droplets when the person coughs or sneezes and is highly infectious. It’s a vaccine-preventable disease, and currently, immunization is recommended with Tdap (Tetanus and pertussis vax) every ten years to boost immunity against both.
Finally, with lower vaccination rates, measles is surging in many countries. In only the first three months of 2024, 56,634 measles cases and four deaths were reported in Europe. Measles is highly transmissible, infecting 90% of those exposed. It’s not a benign childhood infection—measles can cause pneumonia, encephalitis and death.
The latest prediction is that around 11.5 million tourists will descend on Paris for the Olympics. I prefer watching from my quiet home.
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