Water borne diseases and diagnosis
Water-borne diseases are diseases caused due to consumption of contaminated water. Waterborne diseases are very common but often unrecognized. Occurrence is worldwide and the incidence varies from country to country.
Facts and figures on water quality and health (WHO)
- No safe drinking-water: almost 1 billion people lack access to an improved supply
- Diarrhoeal disease: 2 million annual deaths attributable to unsafe water, sanitation and hygiene
- Cholera: more than 50 countries still report cholera to WHO
- Cancer and tooth/skeletal damage: millions exposed to unsafe levels of naturally-occurring arsenic and fluoride
- Schistosomiasis: an estimated 260 million infected
- Emerging challenges: increasing use of wastewater in agriculture is important for livelihood opportunities, but also associated with serious public health risks
Infectious & other causative agents
The most frequent causes of water-borne illnesses are various bacteria, viruses and parasites.
- heavy metal poisoning, including, cadmium, copper, lead, tin and zinc
- toxic cyanobacteria (blue green algae) overgrowth in water.
damage to gut wall and/or systemic infection:
- Salmonella spp.
- Shigella spp.
- Clostridium perfringens
- Campylobacter spp.
- Helicobacter pylori
- Vibrio cholera/V. parahaemolyticus
- Yersinia enterocolitica
- Brucella spp.
- Listeria monocytogenes
- Hepatitis A and E viruses
- Noroviruses and other small round structured viruses (SRSV)
- Cryptosporidium spp.
- Giardia lamblia
The most prominent symptom is acute diarrhea, with nausea, vomiting, abdominal pain but the associated dehydration may lead to electrolyte irregularities, acute renal failure, and encephalopathy. Rarely, waterborne illness may be associated with prolonged or more severe complications, such as anemia, shock, hemolytic–uremic syndrome, spontaneous abortion, seizures, and liver, heart, or lung disease.
Nondiarrhoeal waterborne diseases include listeriosis; hepatitis A etc. Systemic involvement is seen in these diseases.
Mode of transmission
Transmission is predominantly via the faecal-oral route or ingestion of contaminated food and water sources. Transmission via aerosols (produced during profuse vomiting) has been implicated in outbreaks involving viral pathogens.
Foodborne and Waterborne Illness: Diagnosis
- A detailed history to assess changes in the patient’s bowel pattern.
- Acute diarrhea diagnosis in the clinical setting is based on an increased frequency and looser consistency of stools.
- Temporal relationships with exposures to food, antibiotics, sick persons, or travel (including hiking and camping) is important.
- The history may help determine whether the condition is likely to be self limited or requires treatment.
- In addition, the history points toward likely causative organisms that may be candidates for testing.
- For example, a history of blood or mucus in the diarrhea warrants stool examination.
- Stool culture: Stool culture is a test used for the isolation of diarrhea causing organisms from liquid stools. Special nutritional media are used to ensure growth of bacterial pathogens such as Vibrio cholera, Salmonella spp; Shigellaspp.etc.
- Mass spectrometry based systems are helpful in rapid identification of bacteria.
- If antibiotic treatment is needed in severe disease, susceptibility testing can be done using disc diffusion and automated microdilution testing.
- Leukocyte count : Indicate infectious origin especially bacterial diarrhea
- Fecal occult blood testing: May indicate dysentery (blood in stools) due to certain bacteria such as Shigellaspp, E.coli 157.
- Screening for ova and parasites: Saline and iodine mounts are done to detect parasitic infections such as Amoebiasis, Hookworm infections.
- Comprehensive testing for Stool parasites: Includes special stains such as trichrome stain to diagnose parasitic infections.
- Special stains for opportunistic pathogens: Stains such as Mod.Kinyoun, Mod.Trichrome are used to detect parasitic infections in immunocompromised patients.
- Stool antigen tests: Stool antigen tests provide rapid, sensitive and reliable diagnosis of parasites such as Giardia, Cryptosporidium. Also useful in viral disease such as Rotavirus, Norovirus and Adenovirus which are being increasingly recognized as leading causes of diarrhea.
- Serology testing: Serology testing using paired sera is useful for detection of antibodies to various bacteria, virus and parasitic infections, especially in nondiarrhoeal systemic disease.
- Toxoplasma antibodies, Hepatitis A antibodies, Brucella antibodies can be detected by this test.
- Blood culture and other sterile site sample cultures: Used to diagnose infections such as Listeriosis, Brucella spp.
Prevention of the contamination of potable water is very important. Contaminated water should be treated by adequate filtration and disinfection or by boiling.
Vaccines are currently available for cholera and hepatitis A
Food and water-borne outbreaks are usually detected following the onset of illness in a group of people who have shared a common meal. The primary objectives of outbreak control are the rapid identification of the causative agent through epidemiological, environmental and laboratory investigations and prevention of further disease by destruction or denaturation of the source.
International outbreaks are increasingly being recognised, primarily due to the increased trade in food and agricultural products worldwide. Food and water-borne pathogens and contaminants have been identified as potential biological terrorism agents. Cases of rare diseases like botulism should be investigated immediately. Some diseases require notification to the World Health Organization, like cholera.