Swimming in the Seine isn’t the only health risk for Olympians and fans in Paris

This past week, Paris Mayor Anna Hidalgo and other officials swam in the Seine to reassure Olympic participants and the public that the river is safe and that pollution has been cleaned up. With all the talk about the dangers of swimming in the Seine, it’s a good time to mention other health risks for the crowds of visitors who travel to Paris.

Dengue

Dengue and other arboviral infections are of particular concern. Last September, several people with no travel history became ill with dengue in Paris. This showed for the first time that dengue can be transmitted locally in Northern Europe. The number of dengue cases is steadily rising worldwide, from 5.2 million cases in 2016 to almost 10.5 million in America in 2024.

Dengue is transmitted by Aedes albopictus, the tiger mosquito, which feeds on humans. The tiger mosquito is especially problematic because it only needs small amounts of water (e.g. a cap) for its eggs, which can dry out for months. In particular, the The dengue virus can be passed on from the mother mozzie through her eggs. When it rains again, the eggs revive and hatch, starting a new breeding and infection cycle.

Many athletes will come to 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 flu

According to the World Health Organization, influenza activity has increased, with the A(H3N2) virus from South America and the A(H1N1) virus in Africa and Oceania.

The number of weekly new cases of Covid is high, especially in the Great Britain, Portugal and Greecein Europe and China, Thailand and New Zealand. SARS-CoV-2 wastewater levels are rising again in much of the U.S. Mike Hoerger, Ph.D., Covid Predictornotes that current transmission is >3x higher than normal for this time of year.

Many Olympic and Tour de France athletes wear masks to protect themselves from infection after years of training for the events. Masking will be mandatory for the Belgian team. Five of the 176 riders in the Tour dropped out due to Covid infections. Two Swiss Olympic mountains cyclists have already withdrawn due to illnessa shave British athletes Holly Bradshaw & Sarah McDonald.

The The Olympic Games are expected to attract 15 million visitors, 2 million from outside the region. Given the experience of Taylor Swift concerts, which were apparently superspreader events, you might expect a Covid outbreak to occur in these crowded venues. Covid can also be transmitted outdoors, in crowded conditions.

The water quality of the Seine

The Seine has been off-limits to swimming for more than 100 years due to the river’s pollution levels. Historically, runoff mixes with stormwater and is dumped directly into the river after heavy rainfall. Massive efforts were made to clean up the pollution, including the construction of a massive rainwater storage facility, which contained the equivalent of twenty Olympic-sized swimming pools. These costs at least ($1.55 billion).

To reassure the public about the safety of the Seine, Mayor Anna Hidalgo and others took a dip in the river this week. They felt ‘safe’ in this regard, as the number of E. coli bacteria had dropped significantly on Tuesday, after a significant peak the previous Friday due to a large rain shower. The reported levels were below the World Triathlon Federation limits of 1000 CFU/100 ml.

French officials should not be so reassured by these counts. Fluidion, a water intelligence company with headquarters in Paris and Los Angeles, tested the Seine River and made its data available for open access. Fluidion uses a new technology that can provide additional insight into water quality, such as measuring both the “free” (or plankton) count of E. coli bacteria and the expanded count of E. coli bacteria, including bacteria that have aggregated with fecal particles and other sewage.

Dan Angelescu, founder and CEO of Fluidion, explained via email that standard microbiology laboratory methods are designed for water 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 picture of the actual risk.

Although the weather gods seem to be favorable to Paris high temperatures only in the mid-80s and scant rain during the Olympics, other concerns remain.

Water quality has plagued other Olympics. For example, the 2016 Olympics in Brazil raised concerns about “Rio Sewercide” and athletes at risk of multidrug-resistant (CRE) infections from the dirty water.

Leptospirosis remains a concern because it takes very few bacteria to cause this infection. All participants in freshwater sports are at risk of this infection, transmitted by infected animal urine that contaminates the water. Rodents are often the source. Outbreaks have occurred after floods and a whitewater rafting trip. Symptoms include headache, fever, muscle pain 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 is likely to worsen this year, causing significant respiratory problems and illnesses.

The air pollution is also likely to worsen 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 gastrointestinal bugs such as norovirus are to be expected.

Whooping cough (whooping cough) is experiencing a resurgence in Europe. the European Center for Disease Prevention and Control recorded 25,130 cases of whooping cough in 2023, compared to 32,037 cases between January 1 and March 31, 2024. In France, there were more than 5,800 cases 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 contagious. It is a vaccine preventable disease and immunization is currently recommended Tdap (tetanus and whooping cough vax) every ten years to boost immunity against both.

Finally, with lower vaccination rates, the measles is increasing in many countries. In the first three months of 2024 alone, 56,634 measles cases and four deaths were reported in Europe. Measles is highly transmissible, infects 90% of those exposed. It is not a benign infection in children; measles can cause pneumonia, encephalitis and death.

The latest prediction is that approximately 11.5 million tourists will descend on Paris for the Olympic Games. I prefer to watch from my quiet home.