Why You Should Think Twice Before Getting in a Pool 進泳池前為何要三思

薩拉·喬多什 王妍 肖維青

Pools are festering， pathogenic baths that we fool ourselves into thinking are clean.游泳池讓人皮膚感染，引發(fā)疾病，但人們常常自欺欺人地以為泳池很干凈。

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.

游泳池的水聞起來像消毒劑。這種濃郁的漂白粉味道讓人望而生畏，進而讓你相信有人專門設計了這種水體供人游泳。水中加入了氯氣就一定干凈。你聞聞看。

但不幸的是，水中大量加入氯氣并不能保證人們的安全（而且很多人還會在里面小便）。若說有區(qū)別，那就是比起自然水體，人更容易因泳池中的病原體而患病。這是根據(jù)美國疾病控制中心（CDC）最近兩項關于處理與未處理“娛樂用水”的研究得出的結論。

CDC通常會追蹤病原體引起的類似的傳染病爆發(fā)，但隨著耐氯性細菌造成的危害越來越大，他們已經(jīng)開始更加密切地監(jiān)測水源性傳染病。CDC的研究人員指出，耐氯性細菌是現(xiàn)在疫情爆發(fā)的主要原因。你可能會好奇，所以解釋一下，“疫情爆發(fā)”是指兩個或兩個以上的人在同一地點、同一時間段內患上類似的疾病。2000年到2014年期間，在泳池、熱水浴池、水療中心或水上游樂場等場所因處理過的娛樂用水而引發(fā)的疫情為493起，造成27219人染病、8人死亡。8人死亡！

同一時期，因湖泊、河流或海洋等未經(jīng)處理的水而引發(fā)的疫情只有140起，4958人染病，2人死亡。

由于無法準確了解有多少美國人去過經(jīng)處理和未處理的水域，我們無法判斷這項研究結論是否說明游泳池在本質上比湖泊更危險。有一些粗略的估算，美國人口普查局的一項數(shù)據(jù)摘要顯示，總人數(shù)達到了3.01億，但精確的數(shù)據(jù)幾乎不可能得到。CDC的研究人員指出，他們甚至可能無法得出準確的患病人數(shù)，因為需要有人向他們報告這些信息。我們能知道的是，大約有30.9萬個公共游泳池和1040萬個住宅游泳池，但跟蹤到訪每條河流、每個湖泊、每片大海，以及游泳池、熱水浴池和水療中心的準確人數(shù)，這是一項巨大的工程。

但是，在酒店得病的人似乎比在海灘得病的多得多。

這里并不是要你喝未經(jīng)過濾的天然水（即硅谷人所說的“原水”）。溪流湖泊中的水可能含有周圍土壤滲入的農(nóng)藥等化學物質，還有隨動物糞便混入水中的細菌。這就是為什么我們把制定《安全飲用水法》放在首位——飲用水不經(jīng)適當消毒，很容易造成重大公共衛(wèi)生隱患。

盡管人們在經(jīng)處理和未處理水域中感染疾病的類型不同，但有一點相同，那就是糞便，人類的排泄物。大部分致病的病原體通過糞口途徑傳播，這意味著病原體攜帶者在游泳時，體內的病菌通過肛門進入水中，之后其他人會吞入帶有病菌的水或吸入帶有病菌的飛沫。比如，消毒處理過的水體導致的疾病中，80%是由隱孢子蟲引起的，這種腸道寄生蟲經(jīng)由糞便進入水源。未經(jīng)處理的水體導致的疾病種類更多，但罪魁禍首往往仍來自糞便。諾如病毒是最主要的致病原因，在所有病例中大約占30%，經(jīng)由嘔吐物和糞便傳播。志賀氏菌是最常見的細菌感染源，通過腹瀉傳播。

氯氣可以控制泳池和水療中其他許多致病的病原體，但隱孢子蟲能在氯氣消毒的水中存活一周以上，這使它很容易傳給任何一個在這片水域中游泳的人，再由這些人在其他水域游泳時傳播出去。疫情就是這樣爆發(fā)的。

如果你現(xiàn)在和我一樣擔心在公共場所游泳是否安全，最好的辦法是避開酒店（特別是酒店熱水浴池）。32%的疫情爆發(fā)在酒店，其中約40%與熱水浴池或水療中心有關。這些只是CDC可以確定的由病原體導致的疫情的爆發(fā)。在其他不明致病原因的疫情中，50%來自酒店。溫水加上人員繁雜是問題所在，特別是當工作人員沒有正確加入氯氣消毒，情況會更糟。公共游泳池排在第二位，占比23%，其次是水上俱樂部或娛樂設施，占比14%。

避免疫情最簡單的辦法就是不要去公共泳池，這或許說易行難。炎熱的夏天，泳池可是解暑的好去處。對很多人來說，到當?shù)氐挠斡境赜斡?，既是七八月份主要的社交活動，也是消暑納涼的絕佳方式。如果是一個有責任感的人或盡職的家長，請不要讓任何近期腹瀉的人去游泳。除此之外，CDC還推薦另一種方法——準備一些試紙。這些供泳池檢測氯氣含量和PH值的試紙可以在游泳用品店和五金店買到，輕便易攜，所以能裝在游泳包中帶進泳池，養(yǎng)成檢測泳池水的習慣。如果發(fā)現(xiàn)水中的氯氣含量不足，請向工作人員報告，還可以和當?shù)氐臋z測標準進行對照。

如果你有幸住在海邊、河邊或者湖邊，去那里游泳吧。游泳人多的水域都可能充滿潛在的病原體，但至少水域越寬廣，病原體濃度越低。人大小便中的各種病原體會擴散到大得多的水域，你吞下寄生蟲或細菌的可能性也會隨之變小。如果必須去酒店的游泳池，至少避開熱水浴池。? ? ? ? ? ? ? ? ? □

（譯者單位：上海外國語大學）