15. Diarrheal Diseases Flashcards
Agent (3 types)
- Bacterial
- Enterotoxigenic E. coli (致病性大肠杆菌)
- Vibrio cholerae (霍乱弧菌)
- Salmonella (沙门氏菌)
- Shigella (痢疾杆菌)
- Campylobacter (弯曲杆菌)
- Viral
- Rotavirus (轮状病毒)
- Norovirus (诺如病毒)
- Parasitic
- Cryptosporidium parvum (小隐孢子虫)
- Giardia lamblia (蓝氏贾第鞭毛虫)
- Entamoeba histolytica (赤痢变形虫)
Transmission routes
1. Waterborne
- documented for most enteropathogens; for some (e.g. V. cholera) it is the predominant form
- Infectious agents are introduced into water source when people or animals defecate in or near that water source
- The use of contaminated sources of water for bathing, washing, swimming, cleaning, and consumption have been implicated in transmission
- Poor handling practices of water stored in the home increases risk
2. Foodborne
- Fruits & vegetables can become contaminated when irrigated with contaminated water or improperly handled in the home
- In developing countries, most uncooked food should be assumed to be contaminated
- In developed countries, some foods should be assumed to be contaminated (e.g. chicken with Salmonella, beef with E.coli)
- In developed countries, the large-scale production & distribution of food makes contamination more likely and more widespread
3. Person-to person due to poor hygiene
- Increased risk of diarrhea with inadequate handwashing after defecation or cleaning a child
- Improper disposal of fecal material
- defecation in the yard/open areas and nonhygienic methods of feces disposal
- Crawling infants who come in contact with feces on the ground are at particular risk
Population at Risk
children under 5 years of age
Elderly adults due decreased immune function (More pronounced among residents of long-term care facilities)
Individuals who travel to developing countries
about half of travelers will develop diarrhea during a trip of approx. 2 weeks
clinical features (symptoms for 5 diarrhea)
Acute watery diarrhea
- Bacterial or viral etiologies predominate
- Can range in symptomatology from mild (loose stools) to profuse dehydrating diarrhea (severe cholera or ETEC)
Dysentery
- primarily bacterial
- Stools with blood + mucous
Persistent diarrhea
- primarily bacterial and parasitic
- Characterized by watery diarrhea > 14 days duration
Other presenting symptoms
- Vomiting (May be seen with various etiologies; a predominance of vomiting over diarrhea suggestive of viral etiology)
- Fever
- Abdominal cramps
Life threatening diarrhea
- Second leading cause of death in children under 5 years
- Most people who die from diarrhea die from severe dehydration and fluid loss
- Children who are malnourished or individuals with impaired immunity (especially HIV) are most at risk of life-threatening diarrhea
host Risk factors
Malnutrition
- Malnutrition and diarrheal disease coexist in children living in poor developing countries
- Malnutrition is thought to be a direct risk factor for diarrhea through compromised immunologic function
- Malnourished children in developing countries have been found to have a 70% higher risk for diarrhea as well as longer diarrhea episodes of greater severity
Compromised immune systems
- Individuals have reduced resistance to enteric infections
Specific Micronutrient Deficiencies
- Vitamin A deficiency – associated with more severe diarrhea. Populations deficient who receive treatment experience reduced mortality
- Zinc deficiency – associated with more and lengthier episodes of diarrhea. Populations deficient who receive treatment experience reduction in incidence and duration of illness
epidemiology (globe and U.S.)
Globally, there are nearly 1.7 billion cases of diarrheal disease annually. Diarrhea is the second leading cause of death among children under 5 years old. Diarrhea is the leading cause of malnutrition in children under 5 years old.
In the U.S., CDC estimates 21-37 million episodes of diarrhea each year in children under 5 years of age.
Top 5 Foodborne Pathogens: • Norovirus • Salmonella • Clostridium perfringens • Campylobacter • Staphylococcus aureus (金黄色葡萄球菌）
Enterotoxigenic E. coli (ETEC)
致病性大肠杆菌
epi, agent, symptoms, diagnosis, treatment
Epi:
Most frequent cause of diarrheal disease in children in developing countries. Leading cause of travelers’ diarrhea.
Agent: Bacterial agent
Symptoms: profuse watery diarrhea and abdominal cramping
Diagnosis: bacterial stool culture
Treatment: supportive measures; typically don’t require hospitalization or antibiotic
Vibrio Cholerae
霍乱弧菌
epi, agent, symptoms, treatment
Epi:
- Has been causing epidemics for centuries; epidemics result in high mortality.
- In epidemics, feces of infected person contaminates water/food.
- cholera can spread quickly in areas with inadequate treatment of sewage and drinking water.
Agent: Bacterial agent
Symptoms: causes cholera. Infection may be mild or asymptomatic. Approximately 5-10% of infected persons will develop severe disease involving profuse watery diarrhea, vomiting and leg cramps. rapid loss of body fluids. dehydration and shock. death if not treated properly
Treatment: Treatment is oral rehydration (for mild cases) and IV hydration if necessary (for severe cases)
Rotavirus
轮状病毒
epi, agent, symptoms, treatment
Epi:
- The most important viral agent causing diarrheal disease.
- Typically affects children in the first two years of life.
- In U.S., has a winter seasonality (most cases occurring Dec-June)
- In developing countries occurs year-round
Agent: Viral agent
Symptoms: vomiting and watery diarrhea for 3 – 8 days, then resolves
Treatment: nonspecific and consists primarily of oral rehydration therapy to prevent dehydration. In U.S. about 1 out of 70 children with rotavirus disease will require hospitalization for intravenous fluids
Norovirus
诺如病毒
epi, transmission, symptoms, treatment, surveillance
Epi:
- Leading cause of acute gastroenteritis (急性肠胃炎) in all ages in the U.S.
- Leading cause of foodborne illness in the U.S.
- Can occur anytime during the year, but is seen more frequently during the winter
Transmission
- Person to person contact
- Contaminated food or water
- Contaminated surfaces or objects
- Aerosolized vomit
Symptoms: nausea, vomiting, diarrhea & abdominal pain lasting 1-3 days
Treatment: supportive and involves rehydration
Surveillance: CalicNet.
- National norovirus outbreak surveillance network
- Collects data on norovirus strains associated with GI outbreaks in the US
- Public health labs electronically submit lab & epi data to the database
- Helps CDC link outbreaks to a common source
Cryptosporidium parvum
小隐孢子虫
epi, agent, symptoms, diagnosis, treatment
Epi: A leading cause of waterborne disease in the U.S. Often implicated in recreational waterborne outbreaks.
Agent: Microscopic parasite. Parasite is protected by an outer shell that makes it very resistant to chlorine disinfection.
Symptoms:
- Most common symptom is watery diarrhea
- may also involve stomach pains, nausea, vomiting, fever
- Children, pregnant women and immunocompromised can have a more severe course
- Symptoms typically last 1 – 2 weeks, then resolve with supportive treatment
Diagnosis: microscopic examination of stool sample
Treatment: supportive
Treatment for diarrhea
1. Oral rehydration salts (ORS) solution
- A mix of clean water, salt and sugar
- Used to correct dehydration
- ORS is absorbed in the small intestine and replaces the water and electrolytes lost in feces
- Cost is a few cents per treatment
2. Zinc supplements (with ORS)
- Studies suggest that zinc + ORS can reduce duration & severity of diarrheal episodes for up to 3 months
- WHO and UNICEF recommend daily zinc supplements for 10-14 days for children with acute diarrhea to reduce severity and reoccurrences in the ensuing 2-3 months
- Progress is needed in the wide-spread implementation of this treatment strategy
3. Rehydration
- Use intravenous fluids
- Used in cases of severe dehydration or shock
4. Nutrient-rich foods (difficult in poor nations)
- Continuing to give nutrient-rich foods (including breastmilk) during diarrhea episode can help break the vicious cycle of malnutrition and diarrhea
- Feeding a nutritious diet to children when they are well can help decrease a child’s risk of diarrhea
Prevention measures for diarrhea
Access to safe drinking-water
Use of improved sanitation
Hand washing with soap
Good personal and food hygiene
Health education about how infections spread
Breastfeeding
Rotavirus vaccination
Breastfeeding
Breastfeeding, especially exclusive breastfeeding in the first 6 months of life and any breastfeeding in children from 6 -23 months of age reduces diarrhea incidence in infancy and improves diarrhea mortality rates
Breastfed children are exposed to fewer enteropathogens that may be contaminating food and water
Breastmilk may also provide passive immunologic protection
In developing countries, the incidence of diarrhea increases sharply with the introduction of weaning foods
Rotavirus Vaccine
2 rotavirus vaccines licensed in the U.S
vaccine became available in 2006
Vaccine is given orally to infants starting at 2 months of age
Efficacy studies show that rotavirus vaccine is 85%-98% protective against severe rotavirus disease and 74%-87% protective against rotavirus disease of any severity in the first year after vaccination.
In 2009 the WHO recommended that rotavirus vaccination be included in all national immunization programs
