As I write this I am at 30,000 feet winging my way to Montreal, Canada, where the temperature is below freezing. So what more appropriate topic than microbial hazards of bathing beaches? Maybe it was my foray into the wonderful world of fecal accidents that prompted me to look further into the subject but I found a couple of papers from last year by a groups at Johns Hopkins about the effect of bather density on levels of parasites pathogenic for humans at one particular beach in Maryland, the Hammerman area of Gunpowder Falls State Park in Chase, Maryland in mid to late summer of 2006 (here and here).
Considering that 30% of the US population visits a coastal area beach each year, 42% use recreational water sites and these locales account for 85% of US tourist revenue, you'd think we'd know a lot more about the hazards of recreational water than we do. When a beach is closed, most of the time it is because the waters there have exceeded the state allowed levels of fecal or enteric coliforms (a group of organisms whose presence is thought to signal potential contamination by the feces of warm blooded animals. These organisms are not the pathogens, however, only indicators. Pathogens could be other bacteria, viruses or protozoal parasites. The two papers from the Hopkins group undertook to see if there was a relationship between pathogenic parasites and the number of people at the beach. The answer is not obvious. If the source of pathogens is animals (e.g., aquatic birds or run-off from surrounding land) then there might be little relationship. However even if there is a relationship this does not automatically mean humans are the source. They might just be stirring up the sediment where the bugs are hanging out. The more people, the more the sediment gets stirred up. Wastewater discharges (e.g., combined sewer overflows) is another other possible source.
The parasites in these two papers were of two categories, the known pathogens Cryptosporidium parvum ("Crypto") and Giardia lamblia ("Giardia"); and the more recently discovered microsporidia, Enterocytozoon bieneusi and Encephalitozoon intestinalis. The latter two have been known to cause human disease, especially (but not exclusively) in immunocompromised individuals, but they are hard to test for and identify so we know little about their epidemiology, including where those infected encountered them. Crypto and Giardia, on the other hand, have caused numerous waterborne disease outbreaks (including the largest in US history in Milwaukee in 1993, from Crypto) and both are highly resistant to chlorination. Their cysts can remain viable in a hostile environment as long as a year.
These papers are taken up with technical details relating how the samples were taken, handled and analyzed. These are important because much still needs to be worked out and variations in how these things are done is necessary to compare one study with another. But the bottom line is relatively simple: For either class of parasite there was a significant relationship between levels and the humber of bathers. Samples were taken on busy weekends and compared with lightly populated weekdays. Almost half the samples had microsporidia and levels of Crypto ranged from zero to 42 cysts/liter and Giardia from zero to 33 cysts/liter. How much of this stuff does it take to make you sick. For the microsporidia we aren't sure. We'll need human volunteer feeding studies to nail this down. For Crypto and Giardia it depends on the strain. In some cases the answer is less than 10 cysts.
What is the source? Again, we still aren't sure. These studies show clearly that the turbidity or cloudiness of the water is directly related to bather density. So stirring up sediments is happening and this could be the source. But bathers are also sources. It has been estimated that anal fecal residue shed to water amounts to 0.14 g and may be as high as 10 grams (this is from a paper by Chuck Gerba, Quantitative Microbiology 2:55-68, 2000). Despite this estimates of Crypto and Giardia risk from swimming in lakes is estimated to be pretty low (less than one in ten thousand).
But one of the things these studies show is that there are pathogens in recreational waters even when they meet standards deemed acceptable by state and federal bacterial standards. These beaches were legally open to the public. Thus the bacterial indicator standards are of doubtful protection. It further underlines the commonsense notion that public drinking water sources should be separated from recreational bathing locales.
And there are other possible interventions. Limit the number of bathers, prohibit children in diapers and advise anyone symptomatic to stay away.
As for me, when Mrs. R. and I go on vacation, she goes to the beach and I stay inside in air conditioning, read and listen to music. Now you know why.
While I have not lived in a beach community for years, we in the central parts of the country have to contend with contaminated water just like our coastal neighbors.
Our water is contaminated with septic overflow run off, farm runoff, pesticides, fertilizers, and herbicides. I am pretty sure the fecal material in our local creek (down stream from a cow farm) is a lot higher than 10 grams.
Needless to say, I do not wade the creek in anything less than thigh high rubber boots.
I live in a septic tank subdivision and finally after ten years of showing up with annual samples of the ditch water that G. can identify with regarding the smell the state has ordered the country to put in sewers. This is where the EPA comes in and G. if the water contains more than 100 ppm of fecal coliforms in any state, it empties into the tributary waters or navigable waters of the US and its a consistent pattern from point of source, then you have them by the short hairs.They generally dont go beyond the local point when testing. E.g. if it were a business they would be hammering them individually, if its residences they go to the county/city involved.
The EPA and its a Bush EPA rolled into town, started sampling not only the areas around my subdivision, but everywhere in the county and found that all unincorporated sections were off the scale. Acceptable is less than 100, we were at 20,000 units five years ago and it had surged to 30,000. So they politely told the state that it was going to be a $25,000 a day fine, who in turn passed the buck down to the county and said get sewers in. We all still hav to pay but its cheaper than one bug borne disease fix.
G. that stuff is big time dangerous. Polio, typhoid, are in it. Groundwater intrusion from the surface near well fields (this is where I found the old military dump doing this) and all sorts of things could befall you and your kids. Goofy diseases you might find in a third world nation. One womans kid has been in the hospital for six months with an amoebic disease that started eating the kids intestines from swimming in the creek this past summer during the slackwater times.
Here is what the EPA said to me about it, "If you can smell it, its dangerous and above the acceptable limit."
Belly up to the bar and pay for an independent test -about 600 bucks. Then have the results copied to the county..It establishes the record that is needed later if you have to pull the EPA out. Its like Bird Flu... You dont have it until you are tested for it and someone says that it is--BF.
Revere, at least you boldly go where no blogger (typically) has gone before. It a dirty job, but someone's got to do it, eh?
On a related topic, back country camping used to be fun, but nowadays you have to carry your own water purification gear and chemicals. There's virtually no place in the U.S. where you can't find giardia in the surface water. It can come from almost any mammal..,
Randy, the high school kids from my area test the creek every year and it comes back fine. None of the creatures in it are 6 legged or 3 headed plus all the test results (coordinated with the Indiana DNR and State EPA) are well within range of being safe. I just won't go near it, knowing what is upstream.