6 Important health problems and their causes

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Unit 12: Infectious disease


When you have completed this unit you should be able to:

12-1 Why are infectious diseases becoming important again?

Rapid advances were made in the fight against infectious disease in the 20th century. People understood how microbes were spread and this led to improvements in sanitation in towns and cities, and the introduction of hand washing in healthcare providers. From about 1950 onwards, penicillin became widely available, followed by many other antibiotics, and effective treatment for tuberculosis was developed. Immunisation against most of the deadly childhood illnesses was also introduced around this time. Towards the end of the 20th century, it seemed that major epidemics of infectious disease would become a thing of the past. We now know that is not true, and infectious diseases are likely to be an increasing concern in the next few decades for 2 reasons:

Both of these are related to human and social factors.

12-2 What is an epidemic and what is an outbreak?

An epidemic is the occurrence of disease where the number people affected is in excess of what would normally be expected. There does not have to be a particular number of cases. For example, with a very rare infectious disease like bubonic plague, only a few cases are sufficient to call it an epidemic. Most epidemics involve many cases as seen in the past with measles.

A related term is an outbreak, which has the same definition as an epidemic, but we use the term outbreak when numbers are smaller and the cases occur in a more limited area. An example would be scabies in a school.

Epidemic means that more than the expected number of people are affected by a disease.

12-3 What is a pandemic?

When an epidemic affects many countries in the world, we may call it a pandemic. The important pandemics of recent years are HIV, various strains of influenza such as Swine Flu and Avian Flu, and the Severe Acute Respiratory Distress Syndrome (SARS). All of these examples are called pandemics because they have spread over many countries. An epidemic of Ebola in West Africa in 2014 also caused great concern but because it did not spread outside 3 countries in the same region it was not called a pandemic.

12-4 What does endemic mean?

The word endemic is used to describe the occurrence of an infectious disease in a particular area only where the number of cases is stable and predictable. Tuberculosis, Herpes simplex and tick bite fever can be described as endemic diseases, as long as there is no sudden increase in the number of cases.

When an infectious disease occurs at a stable rate that is persistently high, it may also be called hyperendemic. Tuberculosis in South Africa can be described as hyperendemic.

12-5 Where do epidemic diseases come from?

Epidemics frighten people because they seem to appear from nowhere, affect or kill a lot of people, and then disappear. The science of epidemiology tells us how this happens. Microbes, such as bacteria and viruses, reproduce very quickly and often mutate (this means that their genetic code changes a little, together with their behaviour). A mutated microbe may be better adapted to multiply and survive in a particular environment and may also be able to infect other species. Both cause the infection to spread rapidly.

Many of the microbes that cause human epidemics live in animals, where they appear not to cause any great harm. This is called the “animal reservoir” of a microbe. Most modern epidemics are started when humans come into close contact with microbes in the animal reservoir. An epidemic begins when microbes have mutations that allow them to “cross the species barrier”. The infected humans then transmit the microbe to other humans. Increased contact between humans and the animal reservoir happens when humans start living, farming, or looking for food in areas where there has not been a great human presence. For example:

Most new epidemics come from an animal reservoir.

12-6 How do epidemics spread?

Most epidemics are spread either by droplets in the air from coughing or sneezing, like influenza, or from direct contact with body fluids such as blood or saliva, such as Ebola. Whether or not an infection starts spreading to many other people depends on the number of other people each case infects. Each infected person needs to cause (on average) infection in more than one other person in order for the infection to spread, otherwise it will just die out.

For an epidemic to increase and spread, each case must on average infect more than one other person.

12-7 What determines the severity of an epidemic?

The number of people who become ill in an epidemic is affected by:

The epidemic initially grows, and then starts to die out as the microbe encounters fewer susceptible people, either because those who recover from the illness become resistant, or because the population number falls as a result of so many deaths. Transmission between people may completely stop, or the disease may become endemic and continue to occur at a lower rate as has happened with HIV for example.

The number of other people infected by each person with the disease is determined by how infectious the microbe is and also how many susceptible people that infected person comes into contact with.

12-8 How can epidemics be prevented at their source?

To prevent human transmission at source, it is important to understand where these diseases come from, and this may mean trying to control the way in which humans come into contact with animals. Many of the recent influenza pandemics have originated in East Asia and large, live poultry markets in China seem to be an important reservoir. Controlling or closing poultry markets has had an impact on the spread of influenza, but unfortunately also an impact on people’s livelihoods. Controlling the bush meat trade in Africa is more difficult.

Not all epidemics start as a result of human contact with animals. Others may be waterborne, such as cholera, or insect borne such as yellow fever. Improved sanitation and the control of mosquitoes may reduce outbreaks of these diseases.

Many epidemics can be controlled at source by trying to stop humans coming into contact with microbes in the animal reservoir and protecting water supplies.

12-9 What is the difference between isolation and quarantine?

Once microbes have come into contact with humans and caused infection, it is possible to reduce their spread between humans by reducing the number of susceptible people each infected person comes into contact with. This might involve isolating individuals who are showing symptoms and signs of disease. Isolation means keeping sick people apart from others who are well. If they have care needs, special infection prevention and control techniques should be used to look after them.

If somebody has been in contact with the disease, they may have been infected without yet showing symptoms or signs of disease. When they are required to stay away from others for a period of time in case they develop and possibly spread the disease, it is called quarantine.

Isolation means stopping people with symptoms or signs of disease coming into contact with uninfected people. Quarantine involves observing symptom free people who have come into contact with infected people to see if they develop disease.

12-10 What other public health measures are used to reduce contact between infected and susceptible people?

Other methods include:

It is possible to reduce the spread of disease from human-to-human by isolating infected cases, by observing people who might be infected, by looking for contacts, and by immunising where possible.

12-11 How can a health facility prepare for epidemics?

Many of the infectious diseases presenting to facilities in South Africa, such as TB and HIV, are well-known and most service providers are able to take the necessary precautions and deal with them. Occasionally, there are risks from less familiar infectious diseases and we must be prepared for them. These risks are likely to come from acute respiratory viruses, such as the various new types of influenza, or from viral haemorrhagic fevers such as Congo fever and Ebola. Although epidemic management will vary according to the specific threat, there are certain principles that are worth mentioning:

When there is a concern about an infectious disease epidemic in a country or region, it is important for clinical managers to ask for a case definition and a management plan from the district or regional public health team. This must be communicated with the rest of the health team.

12-12 What is an antimicrobial?

An antimicrobial is an agent that either kills microbes (microorganisms) or stops them growing. There are several different types of antimicrobials:

An antimicrobial kills or stops the growth of microbes.

12-13 What is antimicrobial resistance?

Antimicrobial resistance refers to changes in the characteristics of a microbe so that antibiotics, antivirals or antifungals are no longer effective in killing it or stopping its growth.

Most microbes multiply rapidly, and slight changes in their genetic code during this multiplication (“mutations”) give rise to offspring with different characteristics. This means that these microbes can adapt to new environments where they can survive and continue to multiply:

12-14 What factors favour the development of antibiotic resistance?

Resistance is more likely when antibiotics are overused, because the more often bacteria encounter an antibiotic, the more likely it is that an antibiotic will meet mutated bacteria that are resistant to it. When this happens, the resistant bacteria have an advantage and continue to spread and multiply in spite of the antibiotic and becoming the dominant (common) type. There are 2 important reasons for the development of antibiotic resistance:

Resistance is also favoured when antibiotics are taken in a way that only partially treats an infection. This is because bacteria that are partially resistant would have been killed by a full course of treatment but survive and become the dominant type. This often occurs because:

The incorrect use of antibiotics is the main reason why antibiotic resistance develops.

12-15 Why is resistance a problem when new antibiotics can be developed?

Although the pharmaceutical industry continues to produce a stream of new drugs to replace current antibiotics that no longer work, resistance remains a very big concern because:

12-16 Why is a hospital-acquired infection often serious?

The most resistant infections are “hospital-acquired infections” because these bacteria live in an environment where they are exposed to many antibiotics and have the opportunity to acquire resistance to many of them. Infections acquired in intensive care units can be resistant to just about every antibiotic available. Furthermore resistance to antibiotics can spread between different types of bacteria.

12-17 What is the doctor’s responsibility to reduce antibiotic resistance?

Because the problem of antibiotic resistance is potentially so serious, all health workers should be interested in the use of infection prevention and control, using well tested hygiene methods. “Antibiotic stewardship programmes” are hospital based programmes that promote the safe and appropriate use of antibiotics. In this way the use of antibiotics is controlled.

These approaches are described in detail in Infection Prevention and Control of the Bettercare series that is available for free online.

Bacteria develop antibiotic resistance when antibiotics are incorrectly used. Antibiotic stewardship and infection prevention and control procedures can reduce this risk.

12-18 Why is antibiotic resistant tuberculosis becoming common?

Tuberculosis is a bacterial disease that has been with humans since ancient times. Treatment first became available in the 1950s, following the development of streptomycin in 1943. Other TB drugs, including rifampicin were developed in the 1950s and early 1960s.

However, soon after a new drug entered practice, resistance to it was identified. This led to the development of multidrug treatments, so that if a patient was infected with a strain of TB that was resistant to one of the drugs, it would still be killed by at least one of the others. Using a number of antibiotics together therefore reduced the risk of developing resistance. The modern, 4 drug, 6-month treatment regimen was introduced in the 1970s. This was a highly effective treatment for TB and in the 1980s, people started to think that TB could be eradicated as smallpox had been.

What has happened instead is the re-emergence of TB as a major cause of death, particularly in low- and middle-income countries. This is partly caused by social factors and overcrowding, and by HIV, but incompletely treated TB is a serious concern. Many patients stop taking their medication once they feel better and do not complete the full course of treatment. As a result, TB that is resistant to standard drug regimens has emerged. These infections are called:

There have also been reports of “resistance beyond XDR”, which some are calling “totally drug resistant TB”. Public health systems need to be organised so that people are quickly diagnosed, started on an appropriate course of treatment, and complete their treatment. In large parts of South Africa this is not happening.

Case study 1

There had been many outbreaks of Ebola virus before, but these had tended to be confined to small villages in Central Africa. In 2014 there was an epidemic that rapidly spread to several countries in West Africa and many people died. It caused some panic in Europe and North America as there was fear that Ebola might spread worldwide.

1. Why do you think that this epidemic was so much more extensive that previous epidemics?

We have no reason to believe that this virus was more virulent than those causing previous epidemics. It is likely that the rapid spread was because of human and social factors:

Case study 2

In the United Kingdom there was an immunisation scare in the 1990s because the measles-mumps-rubella (MMR) vaccine was said to cause autism in young children. As a result many mothers decided not to have their infants immunised with MMR. In some parts of Wales, only two thirds of children were immunised. For most of the 1990s and early 2000s, there were between 0 and 3 cases of measles confirmed per year for the entire country. However in April 2013, 529 cases were reported.

1. What is the likely cause in the increase of reported cases?

As the rates of measles immunisation in infants dropped, the population of susceptible individuals grew. Eventually, there were enough susceptible individuals for each infected person to spread measles to more than one person and there was an epidemic. Further research showed no link between MMR immunisation and autism.

Case study 3

In July 2014, a Liberian patient collapsed after arriving at an airport in Nigeria and was taken to a hospital with fever and vomiting. The patient said he had malaria. Dr Stella Ameyo Adadevoh recognised the signs of Ebola. She insisted he was hospitalised and that infection control precautions taken while looking after him. He was very angry and needed to be physically restrained. Liberian officials insisted that the patient should be allowed to travel on to a coastal city but Dr Adadevoh refused them permission. The man later died of Ebola and, sadly, so did Dr Adadevoh who became infected. However, by insisting that he was isolated she stopped him carrying the disease into Lagos, a city of 18 million people and probably saved many lives.

1. Dr Adedovah insisted the patient be stopped from coming into contact with other people. Was she ordering him into quarantine or isolation?

Isolation. This person was already showing signs of disease.

Case study 4

In 1981, a cluster of 20 men in New York with Kaposi’s sarcoma was reported.

In 1982, the US Centers for Disease Control (CDC) used the term AIDS to describe the new disease. They reported nearly 600 cases in several cities and said that the incidence was doubling roughly every 6 months.

By the mid-1980s it was clear that the virus had become established in many countries across the globe. In several countries in sub-Saharan Africa, there was an explosive increase in the number of cases.

Although the number of new cases in South Africa is slowly decreasing, HIV infection continues at a predictable rate.

1. What is the best description of the state of HIV infections in South Africa currently? An outbreak, epidemic, pandemic or endemic?

HIV infections now occur at a fairly predictable rate, HIV is best described as endemic in South Africa. The other events described above are epidemics that spread to many countries to become a pandemic.

Unit 13: Non-communicable disease


When you have completed this unit you should be able to:

13-1 What is a non-communicable disease?

A non-communicable disease is a disorder which is usually chronic and cannot be passed from person to person (non-infectious).

13-2 What are the important non-communicable diseases in South Africa?

In common with many other low and middle-income countries, South Africa is experiencing a rising burden of non-communicable diseases. The important contributors are:

13-3 What are the “cardiometabolic” diseases?

The cardiometabolic diseases are a group of conditions associated with a particular high risk lifestyle. They consist of:

These conditions are grouped together because they have the same causes and often occur in the same patient. They are sometimes called “chronic diseases of lifestyle”.

Important cardiometabolic diseases include diabetes, hypertension, coronary artery disease and stroke.

Abnormalities in metabolism such as insulin resistance with impaired glucose intolerance and hyperlipidaemia cause atherosclerotic vascular disease.

13-4 Why are cardiometabolic diseases sometimes called “chronic diseases of lifestyle”?

The “cardiometabolic diseases” are sometimes called “chronic diseases of lifestyle” because they result from a combination of:

An unhealthy diet, too little exercise and obesity are the main causes of “chronic diseases of lifestyle.”

The use of the term “chronic diseases of lifestyle” suggests that the problem is one of self-control and that all that the patient has to do to become healthier is to make better lifestyle choices, but that is not quite true because:

13-5 How do factors during pregnancy affect risk of later cardiometabolic disease?

Low birth weight due to poor intrauterine growth is common in South Africa. It is often a result of poor maternal nutrition, smoking, stress and alcohol or drug use in pregnancy. The growth restricted fetus undergoes changes in the way their genes and cells function that means that they are “programmed” to save energy and survive on a low calorie diet. For thousands of years, this was a useful adaptation because the low-birth weight infant was often born into an environment of scarcity and was more efficient at storing the available energy. However, in the modern world, the low birth weight infant is exposed to high fat, high sugar, modern diets, and is more likely to become an obese adult.

It is also true that obese mothers tend to have obese infants that grow to be obese adults. Therefore both undernutrition and overnutrition during pregnancy can result in children at greater risk of cardiometabolic disease later in life.

Low birth weight babies are “programmed” epigenetically to survive on a low energy diet and therefore are more likely to become obese adults if they have a high calorie diet.

13-6 How important are cancers in low- and middle-income countries?

Reliable cancer statistics can be hard to find from many low- and middle-income countries. Information about cancer in South Africa is collected and published by the National Cancer Registry, but this registry is out of date and not very useful. However worldwide, cancer is said to kill more people than AIDS, malaria and TB combined, with the most common cancers being lung, breast, cervical, bowel, stomach and liver cancer.

13-7 How can cancer be prevented?

Many cancers are preventable:

About 20% of cancer deaths in low- and middle-income countries could be prevented by immunisation.

13-8 What is the burden of chronic lung disease in low- and middle-income countries?

In low- and middle-income countries chronic lung disease is the third most common cause of death after non-communicable disease and cancer.

Three main causes of chronic lung disease in South Africa are:

All are preventable. We also know that chronic lung disease can be improved by good nutrition and lung exercises. Unfortunately access to both may be limited in low income countries.

Chronic lung disease is responsible for about 10% of all DALYs in middle and low income countries.

Smoking is an important cause of chronic lung disease.

13-9 What is the burden of disease from trauma in South Africa?

The main causes of trauma death and injury in South Africa are:

Road accident deaths are nearly twice the global average. For South African males, murder rates are 8 times the global average, and for women are 5 times the global average.

The most recent burden of disease data are from 2000 and show that trauma was responsible for 11.5% of DALYs in South Africa.

13-10 What are the risk factors for trauma deaths?

Trauma deaths and injuries are almost always preventable. The main risk factors are:

13-11 What is the burden of mental health disorders in South Africa?

The simple answer to this is that we do not know. Mental health disorders often go unrecognised and untreated because:

However, it is estimated that 1 in 3 South Africans will have a mental or substance abuse disorder during their lifetime. Over 2% of the population will have post-traumatic stress disorder at some point in their lives. In one study, about two thirds of children had experienced a major traumatic event such as interpersonal violence directed against themselves or a loved one, and 8% met the diagnostic criteria for post-traumatic stress disorder.

A particular problem with mental health disorders is that they can last a long time, there is often delay in diagnosis and treatment and they can recur during the lifetime.

13-12 What are the risk factors for mental health disorders?

The term “mental disorder” covers a broad spectrum of conditions, and much less is known about the causes of mental disorder than is known about disease in other organs. The following are recognised risk factors:

13-13 Apart from mental distress, are there other problems caused by mental health disorders?

Yes. There are other very important consequences of mental health disorders for the individual and for others in the family:

Mental health disorders are common, often undertreated and contribute to the cycle of poverty and ill health.

13-14 What are congenital disorders?

These are abnormalities of structure or function present at birth which result in a wide range of chronic problems.

Structural problems include:

Functional (metabolic) problems include:

As mortality due to infection decreases more childhood deaths are due to congenital disorders.

13-15 What does the “epidemiological transition” mean?

Epidemiology is the study of the distribution of disease and the relationship between risk factors and disease. Poorer countries tend to have a high burden of disease from infections and childhood mortality. As countries become richer, this burden of disease tends to be replaced by chronic non-communicable diseases. This change is called the “epidemiological transition”.

In low and middle-income countries today, there is a rising burden of chronic non-communicable disease while there is still “unfinished business” from the burden of infections and childhood mortality. Therefore the epidemiological transition in low- and middle-income countries has resulted in a “double burden of disease”. South Africans sometimes add maternal and perinatal mortality as well as TB and HIV and describe a “quadruple burden of disease”.

Epidemiological transition means that infections and childhood deaths are replaced by non-communicable diseases as the main causes of death in countries with an increasing standard of living.

13-16 Why are many non-communicable diseases not being prevented?

Great advances have been made in the prevention of infectious diseases over the past 100 years. Health departments are very active in reaching immunisation targets, and epidemics receive national attention. Water quality, sanitation and food safety have improved.

In contrast, little progress has been made in the prevention of chronic non-communicable disease. One of the reasons for this is that many chronic diseases are related to behaviour choices and it is often felt that the chronic disease problems could be solved if only people had the right information and behaved more responsibly. This means that preventative measures for chronic disease tend to be left in the hands of the individual.

Of course, people are ultimately responsible for their own health, but it is important to understand that unhealthy lifestyles are often a result of the environment in which people live. For example, the availability, quality and affordability of foods, family and social norms, advertising, gangsterism and few educational opportunities.

13-17 Can governments do anything about chronic lifestyle diseases?

Yes. Government departments are responsible for the provision and regulation of health services. They can also control people’s exposure to risk factors, including their behaviour choices, using the 3 tools of taxation, legislation and regulation. These are discussed in Part 3: What are the solutions?.

Case study 1

An overweight patient with diabetes has been extensively counselled about the required dietary changes. However, a nurse later sees him in the local supermarket buying chicken wings, a 2 litre cool drink and a large packet of chips for lunch. The following day, the same nurse is on duty in casualty when the patient is admitted with high blood sugar and chest pain.

1. What is the nutritional value of his lunch choice?

The patients needs to lose weight to improve the management of his diabetes but his choice of cool drink, chicken wings and salty chips is not a well-balanced lunch. Chicken wings are high in fat, cool drinks are loaded with sugar, and chips have added salt. These are all foods he should avoid.

2. What other cardiometabolic diseases is this patient at risk of?

The important cardiometabolic diseases are diabetes, hypertension, coronary heart disease and stroke. These are also called chronic diseases of lifestyle. They are usually associated with abdominal obesity, unhealthy diet and too little exercise.

Case study 2

In 2011, the Australian government introduced new legislation that banned cigarette manufacturers from using attractive packaging. Instead, cigarettes could only be sold in plain packets that had graphic photographs of smoking related diseases and warnings about health risks on them. The tobacco giant Philip Morris sued the Australian government. Their argument was that the measure affected their investment and this was a breach of a free trade deal between Pacific Countries. So far, the case has been through the Australian courts and an international court in Hong Kong. The courts have all found in favour of the Australian government. This is a case of a government taking quite radical measures to control the exposure of a population to a risk.

1. Can you think of other risk factors for non-communicable diseases where plain packaging might help?

Plain packaging might reduce the attractiveness of: