Most microbes are harmless or even beneficial, but a small subset—pathogens—can wreak havoc on human health. One of the most common ways people encounter pathogens is through contaminated water. While many water sources undergo treatment that eliminates over 99.9% of microbes, exposure to untreated or improperly treated water through drinking, swimming, bathing, or even inhaling droplets can have devastating consequences. Inadequate access to safe water, sanitation, and hygiene (WASH) has been linked to approximately 1.4 million yearly deaths and 74 million yearly DALYs (disability-adjusted life years). Who are these invisible adversaries, and what diseases do they cause? Explore this lineup to find out—because the first step to defense is knowing your enemy.
Campylobacter jejuni – This mobile, gram-negative, spiral-shaped bacterium can make people ill with campylobacteriosis. This disease causes acute diarrhea, abdominal pain, fever, headache, nausea, and/or vomiting. People are most often infected after eating undercooked meat, but contaminated water is also a frequent source of infection.
Escherichia coli (some) – E. coli are a large and diverse group of Gram-negative, rod-shaped bacteria commonly found in the lower intestine of warm-blooded organisms. Most strains are harmless, but pathogenic strains—including O157:H7, O104:H4, O121, O26, O103, O111, O145, and O104:H21—produce toxins that cause everything from stomach aches to life-threatening complications such as hemolytic-uremic syndrome. Like C. jejuni, these strains can be spread through food (such as unwashed vegetables or poorly prepared meat) and contaminated waters.
Legionella pneumophila – This gram-negative, flagellated bacterium can cause Legionnaires’ disease (severe pneumonia) and Pontiac fever (a milder flu-like illness). Infection typically occurs by inhaling water droplets containing the bacteria, such as from showers, faucets, hot tubs, or air conditioning systems. Other members of the Legionella genus can also cause these diseases in humans, including L. micdadei (Pittsburgh pneumonia agent), L. bozemanii, L. dumoffii, and L. longbeachae.
Leptospira sp. – These spiral-shaped, Gram-negative bacteria cause leptospirosis. Unlike most microbes on this list, leptospirosis is spread through the urine of infected animals rather than feces. The infection can lead to kidney damage, meningitis (inflammation of the membranes around the brain and spinal cord), liver failure, respiratory distress, and even death. About 1 million human cases occur worldwide each year. Cases often increase after hurricanes or floods when large groups are exposed to contaminated water.
Mycobacterium marinum – This is a slow-growing freshwater bacterium that primarily causes skin infections. It must enter the skin through a cut or similar trauma, such as a bite, and can lead to infected granulomas or nodules. In more severe cases, it may cause deeper infections such as tenosynovitis, arthritis, or osteomyelitis.
Salmonella sp. – This large group of rod-shaped, Gram-negative bacteria includes over 2,600 different serotypes, all of which are intracellular pathogens. Salmonella infections are a leading cause of foodborne illness in the U.S. but can also result from drinking contaminated water. Wells are particularly vulnerable to contamination, especially after flooding. The bacteria can also contaminate surface waters—especially those exposed to sewage overflow and agricultural/livestock runoff. Salmonella infections cause diarrhea, fever, and stomach cramps lasting between 4–7 days. Salmonella enterica serotype Typhi causes the more serious typhoid fever.
Shigella sp. – These rod-shaped, nonmotile, facultative anaerobic bacteria are the most common cause of dysentery—an intestinal infection characterized by severe, bloody diarrhea, often accompanied by abdominal cramps, fever, and other symptoms. While dysentery was more prevalent in the past, it remains a serious global health issue. More than 165 million cases occur each year, resulting in approximately 1.1 million deaths. In the U.S., around 450,000 cases of bacterial dysentery are reported annually. While Shigella sp. are the primary cause, dysentery can also be caused by other bacteria, protozoa, parasitic worms, or even certain chemicals.
Vibrio cholerae – This Gram-negative, facultative anaerobic bacterium causes cholera, a disease with a wide range of symptoms. The majority of people infected with V. cholerae experience mild or no symptoms, but about 10% of infections are severe, leading to intense diarrhea, dehydration, and even death. Each year, 1.3–4 million people worldwide contract cholera, and between 21,000–143,000 die from it. Populations with unsafe drinking water, poor sanitation, and inadequate hygiene are at the highest risk.
Vibrio vulnificus and Vibrio alginolyticus – These two species of Gram-negative, saltwater-loving bacteria cause skin infections. V. vulnificus can cause wound infections that rapidly lead to tissue necrosis and septicemia (blood poisoning). V. alginolyticus typically causes milder wound infections as well as ear infections.
This list barely scratches the surface. While these bacteria are among the most common and dangerous, they’re far from the only pathogenic bacteria lurking in the water. We haven’t even dipped into the other groups of microbes – viruses, fungi, protozoa, and helminths – that can also wreak havoc (stay tuned). In fact, there are an estimated 1407 species of waterborne pathogens that can infect humans.
How do we keep one of life’s most essential resources safe from this massive microbial most-wanted list? The answer lies in treatment and in smart surveillance. However, the latter seems like a herculean task. Imagine testing thousands of samples from across the nation and globe, each potentially harboring any combination of those 1,407 pathogenic species, and each requiring close to daily monitoring! Fortunately, indicator species and biotechnology have made this challenge not only feasible but also highly effective. Want to learn more? Dive into this post—or better yet, explore for yourself with one of our water monitoring kits (Chromogenic Analysis of Water Contaminants or Multiplex PCR Testing of Water Contaminants).
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