Your shower may not be getting you as clean as you think with a U.S. study finding many showerheads are dirty and may be covering you in a daily dose of bacteria that could make you sick.

An analysis of 50 showerheads from nine U.S. cities found that about 30 percent harbored high levels of Mycobacterium avium -- a group of bacteria that can cause lung infections when inhaled or swallowed. Researchers from the University of Colorado at Boulder found the levels of Mycobacterium avium were 100 times higher than those found in typical household water.

"If you are getting a face full of water when you first turn your shower on, that means you are probably getting a particularly high load of Mycobacterium avium, which may not be too healthy," said researcher Norman Pace in a statement.

Mycobacterium avium is linked to pulmonary disease, causing symptoms such as a persistent drug cough, breathlessness and fatigue, and most often infects people with compromised immune system but can occasionally infect healthy people.

Pace said research at the National Jewish Hospital in Denver found that increases in pulmonary infections in the United States in recent decades from so-called "non-tuberculosis" mycobacteria species like Mycobacterium avium may be linked to people taking more showers and fewer baths.

He said water spurting from showerheads can distribute pathogen-filled droplets that suspend themselves in the air and can easily be inhaled into the deepest parts of the lungs.

The problem with showerheads is that the insides provide a moist, warm, dark haven where bacteria can form sticky "biofilms" that allow them to gain a foothold and eventually set up residence in the device.

The researchers, however, said it was still probably safe for most people to get into the shower and recommended people with compromised immune systems due to HIV or immune-suppressing drugs, use metal showerheads and change them regularly.

"This really shouldn't concern average, healthy people. The main concern is for people who are immune-compromised," researcher Leah Feazel told Reuters Health. The findings, published in Proceedings of the National Academy of Sciences on Monday, are based on tests of about 50 showerheads taken from nine U.S. cities, including New York, Denver and Chicago.

The researchers said showerheads are not the only potential bacterial dispersants in the home, however.

Feazel said more research is needed to measure bacteria levels in household devices like humidifiers and evaporative coolers.

根据美国一项研究发现：浴室喷头非常脏，带有致病的日剂量细菌。所以洗澡可并不是你想象的那么洁净。

一项对来自9个美国城市50个喷头的研究中，30%隐藏着高含量的结核杆菌-- 一种若被人体吸入或吞食就可能引起肺部感染的菌组。美国科罗拉多州立大学的研究人员发现淋浴的结核杆菌比盆浴要高出100倍。

"刚刚拧开喷头你便满脸水珠，那意味着你脸上很有可能具有高含量的结核杆菌，那很不卫生"norman陈词到。

结核杆菌与肺病密切相关，会引发顽固性咳嗽、呼吸急促、疲劳，大多感染免疫系统遭到破坏的人，偶尔健康的人也会被感染。

Pace 说在丹佛犹太国立医院的研究发现：近十几年由类似分支杆菌属所谓的非结核分支杆菌种类引起的美国肺病的增加与人们平时进行淋浴而不盆浴有关系。

他说从喷头喷出来的水把携带满病原体的水滴雾化到空气中，就很容易被吸进肺部深处。

淋浴喷头的问题就在：它里面提供细菌形成粘膜的潮湿、暖和、黑暗的生长环境，使得细菌在此有立脚点，最终在此长期居住。

研究人员建议说对于大部分人来说淋浴还是安全的，但建议由HIV或服用免疫镇压剂导致免疫系统受损者使用金属喷头并要经常更换。

"其实这并不影响正常健康的人，主要影响免疫系统受损者"Leah Feazel研究员告诉鲁特健康所说。该发现发表在国家科学学会公报上的发现主要是基于对美国包括纽约、丹佛、芝加哥等9个城市50个喷头的调查。

但研究员们还说喷头并不是家里唯一的细菌扩散器，Feazel 说 仍需更多对像加湿器和蒸发式冷却器的家用设备研究来测量细菌的含量水平。