Study Session 33 Bacterial and Viral Faeco-Oral Diseases
In the previous study session you learnt about the general features of faeco-oral diseases. With that introduction in mind, we will now discuss the common faeco-oral diseases caused by bacteria and viruses. In Study Session 34, you will learn about faeco-oral diseases caused by protozoa and intestinal worms. The conditions covered in this study session are divided into two groups: bacterial and viral faeco-oral diseases characterised by diarrhoea, and those characterised by high fever.
We begin with three diarrhoeal diseases: cholera, shigellosis and rotavirus infections. In each case, you will learn about their specific infectious agents, occurrence, modes of transmission, symptoms and signs. Then we remind you of the common features of the diagnosis and treatment, prevention and control of diarrhoeal diseases, which you already studied in general terms in Study Session 32. Finally, we describe the febrile illness, typhoid fever, which is also transmitted by the faeco-oral route. The focus of discussion in this study session will be on aspects that will be especially important to you in your daily work as a Health Extension Practitioner.
Learning Outcomes for Study Session 33
When you have studied this session, you should be able to:
33.1 Define and use correctly all of the key words printed in bold.
(SAQs 33.1, 33.2 and 33.4)
33.2 Describe the most common types of bacterial and viral faeco-oral diseases, their causative infectious agents and their occurrence in the population. (SAQs 33.1 and 33.3)
33.3 Describe the main modes of transmission of each of the bacterial and viral faeco-oral diseases, and the age groups that are most susceptible to them. (SAQs 33.3 and 33.4)
33.4 Explain how you would diagnose and treat cases of bacterial and viral faeco-oral diseases, and when and why you would refer them to a higher-level health facility. (SAQs 33.2 and 33.4)
33.5 Describe how you would apply prevention and control measures against bacterial and viral faeco-oral diseases, and what actions you would take to prevent epidemics of cholera or shigellosis. (SAQs 33.2 and 33.4)
We begin by discussing cholera – its infectious agent, occurrence, symptoms and signs. Knowing about the nature of cholera will help you to diagnose, treat, prevent and control this disease, as described in Sections 33.5 and 33.6, together with measures against all the other bacterial and viral diarrhoeal diseases.
33.1.1 Infectious agents and occurrence of cholera
What comes to your mind when hear the word cholera? It is an acute diarrhoeal disease that affects the intestines and can kill vulnerable patients within a few hours if they are not treated quickly. The WHO estimates that there are 3 to 5 million cases of cholera every year around the world, and between 100,000 to 120,000 deaths. It can affect people in all age-groups. Cholera is caused by the bacteria namedVibrio cholerae (Figure 33.1), which occur naturally in the environment in shallow water around coasts, particularly where rivers flow into the sea. However, people infected by cholera bacteria can rapidly spread the organisms anywhere in a country, particularly where faeces leak into waste water collections.
Figure 33.1 Vibrio cholerae bacteria magnified thousands of times.
(Photo: Wikimedia Commons)
33.1.2 Cholera epidemics
Cholera can spread very easily from person to person, because even a few bacteria are enough to cause the disease if the person is already vulnerable, e.g. due to malnutrition or other infections. Although about 75% of people infected with the bacteria do not develop any symptoms, they can still pass on the infection in their faeces for up to two weeks, so epidemics can develop very quickly.
Do you remember the definition of an epidemic? (Think back to Study Session 1 in Part 1 of this Module.)
An epidemic is defined as a sudden rise in the number of cases of a condition, which go on increasing for weeks or months before being brought under control; sometimes the numbers affected in an epidemic can continue rising for years (e.g. HIV/AIDS).
End of answer
There have been epidemics of cholera in Ethiopia; in 1970, several thousand deaths occurred in the eastern, central and southern regions of the country. Conditions leading to epidemics include the consumption of unsafe water, poor hygiene, poor sanitation and crowded living conditions. Cholera often follows after natural disasters involving flooding, and when large numbers of refugees live in camps (Figure 33.2). Consideration of these factors is important for the prevention and control of epidemics of cholera. In Section 35.2 of this study session, we mention the actions that should be taken to prevent a single case from leading to an epidemic. The details of epidemic investigations and management more generally are the subject of Study Session 42.
Figure 33.2 Cholera can spread quickly and cause epidemics in refugee camps, like this one in the Democratic Republic of the Congo.
Knowledge of the typical symptoms and signs of cholera will help you to suspect cases and undertake further epidemic investigation measures. Cholera usually manifests after an incubation period of one to five days (i.e. the time between the bacteria entering the person’s body and the first symptoms appearing), but it can begin within a few hours after the infection. In about 80% of cases, the disease presents with relatively mild symptoms, but about 20% develop acute watery diarrhoea with severe sudden onset. The stools are painless and voluminous, with the appearance of water in which rice has been boiled (rice-water stools are a characteristic sign of cholera). The patient also experiences nausea, vomiting (Figure 33.3), fever and rapid progression to experiencing extreme weakness and shock. In such cases, death may occur within hours after the start of the illness.
Figure 33.3 Profuse vomiting and rice-water stools are characteristic symptoms of cholera.
Shock in cholera results from rapid dehydration and loss of essential salts in the voluminous diarrhoea and vomit. You learned about shock as a result of haemorrhage during and after childbirth in the Modules on Labour and Delivery Care and Postnatal Care. The signs are the same in shock due to severe dehydration caused by cholera.
What are the typical signs of shock in an adult patient?
The typical signs of shock are systolic blood pressure dropping below
90 mmHg and/or diastolic blood pressure dropping below 60 mmHg, with a rapid pulse rate above 100 beats per minute. A person in shock will often appear confused and may lose consciousness. You must act quickly to save their life.
End of answer
If you see a person with the characteristic symptoms and signs of cholera, you must manage the patient immediately and begin effective control measures in the community (as described below in Sections 33.4 and 33.5). The risk of a cholera epidemic developing from a single case is high, so you must also undertake epidemic investigation and management procedures, which will be described for all epidemic conditions in Study Session 42.
Suppose you were called to see an adult with acute watery diarrhoea and profuse vomiting of two days’ duration. What other evidence would suggest a diagnosis of cholera in this person?
In addition to the rapid onset and progression of the illness, the following symptoms and signs would support the diagnosis of cholera:
Painless diarrhoea and rice-water appearance of his stool