Science of Epidemiology

• Edward Truelove

EPIDEMIOLOGY

Introduction

This assignment will identify and explain what epidemiology is and describe how epidemiologists collect and analyse specific data. It will then identify a number of aspects of the science and then look a disease and see how epidemiologist’s data was used to influence health promotion.

What is Epidemiology?

Epidemiology is the ‘science concerned with the study of the factors determining and influencing the frequency and distribution of disease, injury, and other health-related events and their causes in a defined human population. Also, the sum of knowledge gained in such a study’.

There are two main types of Epidemiology. The first one is descriptive which describes the occurrence of the disease according to people, place and time and the second is analytic which determines the causation, risk factors for health, disease and association.

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Descriptive epidemiology describes and investigates the scale of the problem. This is the amount of people that have developed or caught the disease over a specified period. e.g. in 2004 there were 44,659 cases of newly diagnosed breast cancer in the UK. From this epidemiologists would look at the prevalence, the number of people that have the disease or condition at any particular time. e.g. the number of people who are regular smokers within a specified time period. The next factor is to look at how the condition is spread. This is done by analysing categories such as age, gender, socioeconomic class and ethnicity e.g. women from lower social classes are much more likely to smoke than women in higher social classes.

Examples of questions asked to collect this data are as follows:

• What are the health problems?
• How many people are affected?
• Who is affected?
• Which communities are affected and why?
• What are the trends?

Answers to these questions can indicate if primary prevention is possible and it can show the seriousness of the problem and how individuals and communities may be affected.

Analytical epidemiology aims to answer the question, why did it happen? This is done by identifying and determining the causes and risk factors for health and disease.

Comparisons have to be made between groups with or without the disease and between groups exposed and not exposed to a possible causal factor.

Causation can show if there is a link from a certain disease to environmental influences, lifestyle or socioeconomic factors. To find the cause, epidemiologists can use inferential statistics to draw inferences about apopulationfrom arandom sample. From analysing the results and assessing the risks, a link between events and contributory factors can be draw and this can vary from negligible to high.

Assessing the needs and analysing the data

The first step in planning health promotion is to assess the needs and this consists of two elements. Firstly are the health service needs, which are determined from health data such as occurrence, frequency, mortality and morbidity. Secondly is the community determined needs covering issues that individuals and communities have brought to the attention of the local authority, politicians and letters etc. Sometimes these two elements overlap but it is important to identify which are priorities for communities.

Health data is analysed according to who has been affected and this shows which communities are affected the most so that resources can be allocated. From this information about prevention begin.

Prevention

Primary prevention consists of trying to keep people healthy and free from disease such as immunization and encouragement of healthy lifestyles. Secondary prevention tries to identify the disease and persuade people to go for treatment at the earliest opportunity. Examples could be a cough that could lead to tuberculosis or a fever that could lead to influenza. In some conditions once the disease has developed it can often be too late, so one of the key roles of health promotion is to encourage screening i.e. breast cancer. Tertiary prevention involves actions if the disease has become very serious. This is to promote recovery and focus on rehabilitation to help speed the recovery. An example of primary prevention would be lung cancer as it is know what causes it, but it is not suitable for breast cancer as the causes are not yet known. Prevention can only take place if the causes can be established.

Causes

Epidemiologists need to establish causes and to look at many factors such as the environment, society and individuals. They also need to find out what causes the cause as there can be a whole chain of causal factors triggering a chain of events.

These study designs are used for finding out possible causes, although they do not prove causal relationships as they just look at associations.

There are two types of analytical study designs. The first is group one which are used for finding out possible causes. Ecological studies compare studies of a particular disease in different communities to try to ascertain the cause.

Cross-sectional studies sample a section of society at one particular time to see if there are common characteristics between people. Case control studies compare a sample of people with a disease to a sample without and a conclusion can be drawn to see if characteristics are more likely to be found in people with the disease.

Group two analytical studies are stronger design studies which are used to provide evidence for causal relationships. Cohort studies, also known as prospective or longitudinal studies are when a large sample of the population is followed over a long period of time to monitor their lifestyle and exposure to the risks. From this, the incidence of the disease can be followed to look for causal risks. Examples of this are following a sample of the population for fifty years to see if there is a link between smoking and lung cancer. Intervention study involves exposing a random selection of people to a health promotion trial to find out if the if intervention has health benefits and then to compare the results to a group of people who have not. Results can be analysed to establish if there are key variable such as income, age, distribution, etc. Relative or attributable risk provides a measure of the strength of a causal relationship. Decisions can be made from this as to how many lives could be saved if the causal factor was removed. Epidemiologists have also to work out which are confounding factors, ones that can appear to be associated with a disease but are not a causal.

From all the information and studies undertaken there has to be a systematic review to identify which studies have strong conclusions. From the evidence, reasons can be worked out for showing the causes of health problems and disease and an action plan for health promotion can be set out.

Epidemiology is an essential key discipline in health promotion and unless the specific factors that cause a health problem are identified, action cannot be taken to prevent it and promote health.

Swine flu and Epidemiology

What are the health problems?

In the case of swine flu, dry cough, sore throat, headache and fatigue are the most common associated symptoms. Typically patients will have a fever over 38C. Most people recover in a week without any specific treatment.

How many are affected

In swine flu the number of cases in the UK rose quickly after the first established cases in Scotland. By May 312009, there were 252 confirmed cases in the UK.Seventy of these had been to Mexico or the US seven days prior to infection, and 178 reported that they had not been abroad.

Who is affected?

In the case of swine flu, in the first months of its outbreak in the UK, it mostly affected young people, and was most commonly spread through contact at schools. These findingsare based on an analysis ofthe first 252 cases of the disease diagnosed in the UK after news of the virus broke

What are the trends?

Of the 168 who contracted the infection it was established the likely place of viral transmission: 60% had been acquired in school; 25% from a household environment;

8% in the community; 1% (two cases) acquired in the workplace; Less than 1% (one case) in a healthcare environment; 5% acquired elsewhere. (nhs.uk)

Which communities are affected and why?

People of all genders and ages, including infants and the elderly were developing the disease equally. Due to a larger proportion of younger people travelling abroad and being in contact with younger people, the average age of the first 252 infected people was 20 years. Of the 178 first cases in the UK, 22% reported contact with someone who had developed the infection overseas (secondary infection) and 70% reported contact with a secondary case. 7% were not aware that they had contacted anyone (nhs.uk)

Influence on health promotion

The disease was first identified in Mexico in April 2009 and quickly spread round the globe. Initially the HNS had to make the public aware of the health problems through the media and do everything to contain the disease such as closing schools. After a while it was classed as a pandemic and moved from a containment status to treatment status. Generally the disease was fairly mild and was usually more serious in patients with other health problems. Part of the health promotion campaign was to offer antiviral medicines, Tamiflu or Relenza.

Another step was to identify who and which communities are affected, and those people that are in high risk groups, as they are more likely to develop to complications. Vulnerable people are those who have lung disease, heart disease, kidney disease, liver disease, neurological disease and diabetes. Also at risk are people who have had drug treatment, pregnant women, people over 65 and children under five.

A health promotion campaign through the Television and media was used to make these particular groups aware of the potential risks. Swine flu vaccination began in October 2009

The NHS issued information to the public to stop the disease spreading such as good respiratory and hand hygiene i.e. sneezing into a tissue and putting it a bin and to wash your hands and work surfaces at home regularly. Other public health information includes a National Pandemic Flu website and telephone number for the public to call for any information. The public were asked to call their GP if they had flu like symptoms and particularly if they had a serious condition that weakens your immune system, if they are pregnant, have a sick child under one or if the condition suddenly gets worse. The Service assesses the symptoms and if required will provide authorisation to collect antiviral medicine.

Carers also have been identified as at risk as they come into contact with the most vulnerable in the community and steps have been taken in the second phase of vaccination to protected them from the risk of infection

Conclusion

The science of epidemiology involves elements of biology, social sciences and ecology and it is therefore it is a bio-social-environmental science focusing on disease in populations.

Epidemiology is a key discipline in Health Promotion as is analyses specific factors of a disease. From this data action can be taken to prevent the disease spreading and promote health i.e. smoking and lung cancer, asbestos and cancer, alcohol and liver disease. However, mistakes can be made as some diseases such as heart disease have many influential factors including diet, exercise, smoking, blood pressure and genetic history. Epidemiology is a population science and investigations of health problems in populations have been very important for public health. Its techniques in examining the disease patterns between populations have been widely applied and there is no consensus of the best means to measure health. As epidemiology is a study of populations it does not tailor health promotion needs for the individual and quite often complicated data and government health warnings such ‘eat five portions of fruit and vegetables a day’ can be largely ignored by a sceptical public, and therefore destructive activities still persist.

This report has identified what epidemiology is and explained how epidemiologists assess the spread of illness and analyse data collected. It has also listed aspects of epidemiology and stated how they have an influence on health promotion.

References

• Cancer Research (2009) [Online], Available at: http://info.cancerresearchuk.org/cancerstats/types/lung/incidence/index.htm 1 ( (Accessed 22 Nov 2009)
• Hubley, H. and Copeman, J. (2008) Practical Health Promotion, Polity Press: Cambridge.
• Naidoo, J. and Wills, J. (2009) Foundations for Health Promotion, 3rd Edn, Bailliere Tindall: London.
• Naidoo, J. and Wills, J. (2008) Public Health and Health Promotion, 2nd Edn, Bailliere Tindall: London.
• NHS (2009), [Online], Available at: http://www.nhs.uk/news/2009/07July/Pages/Swinefluearlyepidemiology.aspx 1 (Accessed 2 Dec 2009)
• NHS (2009), [Online], Available at: http://www.nhs.uk/conditions/pandemic-flu/Pages/Introduction.aspx?WT.srch=1 (Accessed 2 Dec 2009)