Why You Should Think Twice Before Getting in a Pool 进泳池前为何要三思

萨拉·乔多什 王妍 肖维青

Pools are festering， pathogenic baths that we fool ourselves into thinking are clean.游泳池讓人皮肤感染，引发疾病，但人们常常自欺欺人地以为泳池很干净。

Pool water smells like disinfectant. It has that cloying， antiseptic aroma that at once deters and reassures you that someone has designed this body of water for you to swim in. It’s got chlorine—it must be clean. Just smell it.

But unfortunately， our liberal use of chlorine in pools isn’t keeping people safe （and all the people peeing in there aren’t helping）. If anything， you’re more likely to get sick from the pathogens in pool water than a natural body of water. That’s according to two recent studies from the Centers for Disease Control （CDC） on treated1 vs. untreated “recreational water.”

The CDC generally tracks outbreaks like this—those caused by pathogens—but they’ve started monitoring water-borne infections more closely because of the rising danger posed by chlorine-tolerant bugs. Researchers at the CDC noted that they are now the leading outbreak cause. An “outbreak，” in case you were wondering， is defined as two or more persons contracting a similar illness from the same location and time of exposure. There were 493 outbreaks caused by treated recreational water from 2000 to 2014 （that’s from a pool， hot tub， spa， or water playground） resulting in 27，219 cases and eight deaths. Eight deaths.

In that same time period there were only 140 outbreaks from nontreated water like lakes or rivers or oceans， and 4，958 cases of illness from those outbreaks. Two people died.

Without knowing exactly how many Americans visited treated versus nontreated water locations， we can’t know whether this means that pools are inherently more dangerous than lakes. There are some rough estimates—one U.S. Census Bureau statistical abstract puts the total number of visits are 301 million—but precise numbers are close to impossible to get. The CDC researchers note that they’re probably not even getting an accurate number of illnesses， since it depends on reporting that information to the CDC itself. We can know that there are about 309，000 public pools and 10.4 million residential ones， but tracking the precise number of visits to every river， lake， ocean， pool， hot tub， and spa would be a massive undertaking.

But many， many more people seem to get sick at hotels than at beaches.

Which is not to say that you should drink unfiltered， naturally occurring water （or “raw water，” as Silicon Valley people call it）. Water in streams and lakes can contain chemicals like pesticides that seep out of the surrounding land， plus bacteria from animal poop that’s in and around the water. That’s why we established the Safe Drinking Water Act in the first place—because drinking water easily poses a major public health risk if not properly sanitized.

Though the kinds of infections people came down with at treated and untreated locations varied， there was one commonality： poop. Human poop. Most of the pathogens causing problems get transmitted via the fecal-oral route， meaning an infected person swims in water and the bug travels from their anus into the water， and then someone else either swallows that water or inhales aerosolized droplets of it. For instance， about 80 percent of the illnesses contracted from treated water were caused by Cryptosporidium， a parasite that lives in animal intestines and spreads by shedding itself from feces into water sources. The illnesses from untreated water were more varied， but the main culprits still tended to come from poop. Norovirus2 was the single biggest contributor， at about 30 percent of all cases， and that’s spread through vomit and feces. The most common bacterial infection， Shigella， spreads through diarrhea.

Chlorine can control many of the other pathogens that made people sick from pools and spas， but Crypto can survive in chlorinated water for more than a week. That makes it easy for the parasite to spread to anyone who swims in that water， and then to anyone who swims in water that all those other infected people swim in. This is how outbreaks happen.

If you， like me， are now worried about swimming in any public place， the best thing to do is avoid hotels （and especially hotel hot tubs）. 32 percent of the outbreaks came from hotels， and of those about 40 percent were associated with hot tubs or spas. And that was just for the outbreaks where the CDC could identify the pathogenic cause. Among unidentified outbreaks， half were from hotels. The combination of warm water and lots of people from lots of places is trouble， especially if the staff doesn’t properly chlorinate their water. Public parks came in second， at 23 percent of outbreaks， followed by 14 percent at clubs or recreational facilities.

Avoiding outbreaks is as simple as avoiding public pools， which is to say simple but perhaps not easy. Summer is hot. Pools are cooling. For a lot of people， the local swimming hole is both the main social activity and the best way to stay out of the heat during July and August. Apart from being a responsible person or parent by not allowing anyone to swim who’s had diarrhea recently， the CDC recommends one other option： get some test strips. Pool supply and hardware stores often carry testing strips for pools that determine chlorine level and pH. They’re light and portable， so you can stash them in your pool bag and make a habit of testing the water. If the pool doesn’t have enough chlorine， report it to the staff. You can also try to check the location’s inspection score.

If you’re lucky enough to live by an ocean， river， or lake—go there. Any water with lots of humans swimming in it is likely full of potential pathogens， but at least in a larger body of water you’ve got the benefit of dilution. Any pathogens from people’s pee and poop will get distributed throughout a much larger volume， thus making it less likely that you’ll swallow parasites or bacteria. And if you must go to a hotel pool， at least stay out of the hot tub.

游泳池的水闻起来像消毒剂。这种浓郁的漂白粉味道让人望而生畏，进而让你相信有人专门设计了这种水体供人游泳。水中加入了氯气就一定干净。你闻闻看。

但不幸的是，水中大量加入氯气并不能保证人们的安全（而且很多人还会在里面小便）。若说有区别，那就是比起自然水体，人更容易因泳池中的病原体而患病。这是根据美国疾病控制中心（CDC）最近两项关于处理与未处理“娱乐用水”的研究得出的结论。

CDC通常会追踪病原体引起的类似的传染病爆发，但随着耐氯性细菌造成的危害越来越大，他们已经开始更加密切地监测水源性传染病。CDC的研究人员指出，耐氯性细菌是现在疫情爆发的主要原因。你可能会好奇，所以解释一下，“疫情爆发”是指两个或两个以上的人在同一地点、同一时间段内患上类似的疾病。2000年到2014年期间，在泳池、热水浴池、水疗中心或水上游乐场等场所因处理过的娱乐用水而引发的疫情为493起，造成27219人染病、8人死亡。8人死亡！

同一时期，因湖泊、河流或海洋等未经处理的水而引发的疫情只有140起，4958人染病，2人死亡。

由于无法准确了解有多少美国人去过经处理和未处理的水域，我们无法判断这项研究结论是否说明游泳池在本质上比湖泊更危险。有一些粗略的估算，美国人口普查局的一项数据摘要显示，总人数达到了3.01亿，但精确的数据几乎不可能得到。CDC的研究人员指出，他们甚至可能无法得出准确的患病人数，因为需要有人向他们报告这些信息。我们能知道的是，大约有30.9万个公共游泳池和1040万个住宅游泳池，但跟踪到访每条河流、每个湖泊、每片大海，以及游泳池、热水浴池和水疗中心的准确人数，这是一项巨大的工程。

但是，在酒店得病的人似乎比在海滩得病的多得多。

这里并不是要你喝未经过滤的天然水（即硅谷人所说的“原水”）。溪流湖泊中的水可能含有周围土壤渗入的农药等化学物质，还有随动物粪便混入水中的细菌。这就是为什么我们把制定《安全饮用水法》放在首位——饮用水不经适当消毒，很容易造成重大公共卫生隐患。

尽管人们在经处理和未处理水域中感染疾病的类型不同，但有一点相同，那就是粪便，人类的排泄物。大部分致病的病原体通过粪口途径传播，这意味着病原体携带者在游泳时，体内的病菌通过肛门进入水中，之后其他人会吞入带有病菌的水或吸入带有病菌的飞沫。比如，消毒处理过的水体导致的疾病中，80%是由隐孢子虫引起的，这种肠道寄生虫经由粪便进入水源。未经处理的水体导致的疾病种类更多，但罪魁祸首往往仍来自粪便。诺如病毒是最主要的致病原因，在所有病例中大约占30%，经由呕吐物和粪便传播。志贺氏菌是最常见的细菌感染源，通过腹泻传播。

氯气可以控制泳池和水疗中其他许多致病的病原体，但隐孢子虫能在氯气消毒的水中存活一周以上，这使它很容易传给任何一个在这片水域中游泳的人，再由这些人在其他水域游泳时传播出去。疫情就是这样爆发的。

如果你现在和我一样担心在公共场所游泳是否安全，最好的办法是避开酒店（特别是酒店热水浴池）。32%的疫情爆发在酒店，其中约40%与热水浴池或水疗中心有关。这些只是CDC可以确定的由病原体导致的疫情的爆发。在其他不明致病原因的疫情中，50%来自酒店。温水加上人员繁杂是问题所在，特别是当工作人员没有正确加入氯气消毒，情況会更糟。公共游泳池排在第二位，占比23%，其次是水上俱乐部或娱乐设施，占比14%。

避免疫情最简单的办法就是不要去公共泳池，这或许说易行难。炎热的夏天，泳池可是解暑的好去处。对很多人来说，到当地的游泳池游泳，既是七八月份主要的社交活动，也是消暑纳凉的绝佳方式。如果是一个有责任感的人或尽职的家长，请不要让任何近期腹泻的人去游泳。除此之外，CDC还推荐另一种方法——准备一些试纸。这些供泳池检测氯气含量和PH值的试纸可以在游泳用品店和五金店买到，轻便易携，所以能装在游泳包中带进泳池，养成检测泳池水的习惯。如果发现水中的氯气含量不足，请向工作人员报告，还可以和当地的检测标准进行对照。

如果你有幸住在海边、河边或者湖边，去那里游泳吧。游泳人多的水域都可能充满潜在的病原体，但至少水域越宽广，病原体浓度越低。人大小便中的各种病原体会扩散到大得多的水域，你吞下寄生虫或细菌的可能性也会随之变小。如果必须去酒店的游泳池，至少避开热水浴池。                  □

（译者单位：上海外国语大学）