Section 2 Diagnosis, Prognosis and Epidemiology

Diagnosis, Prognosis, Morbidity and Mortality

Etiology – Categories of Causes

The causes of diseases, disorders, and syndromes can be organized into the following categories:

• Infectious diseases: caused by viruses, bacteria, fungi, helminths, and protozoa.
• Immune dysfunction:  illness arising from a deficient or overactive immune system (e.g., allergies, autoimmune diseases).
• Trauma:  bone fractures, wounds, injuries.
• Nutritional deficiencies.
• Cancer.
• Lifestyle factors.
• Toxins.
• Genetics.
• Congenital defects.

Genetic Disorders, Hereditary Diseases, and Congenital Defects

Three closely related but distinct terms deserve careful attention:

Examples of genetic disorders you may be familiar with:

• Cystic fibrosis:  recessive, caused by a mutation on chromosome 7.
• Sickle cell anemia: recessive, caused by a mutation in the hemoglobin beta chain gene on chromosome 11.
• Marfan syndrome:  autosomal dominant, mutation on chromosome 15.
• Huntington’s disease:  autosomal dominant, mutation on chromosome 4.
• Down syndrome: inheritance of three copies of chromosome 21 (trisomy 21).

The most common congenital defects include: congenital heart defects, hypospadias (slight misplacement of urethra within penis), clubfoot (inward turn of foot), cleft lip and cleft palate (incomplete fusion of right and left palatine and/or maxillae bones in the roof of the mouth), limb defects, and mental dysfunction.  Many of these can be surgically corrected or managed with physical therapy.

The causes of congenital defects are most often multifactorial – meaning many factors are responsible – including genetic susceptibilities, fetal exposure to teratogens.

Clinical Manifestations – Signs and Symptoms

Idiopathic and Iatrogenic Disease

Predisposing Factors (Risk Factors)

A predisposing factor is another term for risk factor – a condition or characteristic that increases a person’s susceptibility to developing a disease.  Common risk factors include:

• Age:  Older age increases risk for cancer and many other diseases, as a lifetime of exposure to damaging agents accumulates and cells become less effective at providing protection, fighting infection and healing tissue.
• Biological sex: Females are more susceptible to autoimmune diseases and lung cancer.  Males are more susceptible to cardiovascular disease, X-linked colour blindness, and Duchenne muscular dystrophy.
• Genetics:  Certain genetic profiles increase susceptibility (e.g., sickle cell anemia, cystic fibrosis).
• Congenital defects:  Some defects (e.g., congenital heart defects) can make organs less robust and more susceptible to wear and tear, injury and disease.
• Diet:  Malnutrition impairs growth, cognitive function, and organ function globally.  In many Western countries, diets high in fat, sugar, and/or salt increase risk for heart disease, diabetes, and possibly Alzheimer’s disease.
• Occupation:  Exposure to radiation, asbestos coal dust, and pollutants, increases risk for cancers and lung disease.  Pesticide use is being linked to the onset of Parkinson’s disease.
• Location:  Geography determines exposure to local infectious microbes, sociodemographic factors, and cultural practices.  For example, malaria is endemic to tropical regions where the Plasmodium protozoan parasite is carried by specific mosquitoes.

Neglected Tropical Diseases (NTDs)

Neglected Tropical Diseases (NTDs) are a group of diseases most prevalent in the tropics, that despite affecting millions of people each year, lack adequate prevention and treatment strategies.  Malaria and Tuberculosis alone kill 2 million people annually.

These diseases are called neglected because pharmaceutical companies and governments historically direct little research funding toward them by Western nations, partly because these regions are largely unaffected, which additionally makes these treatments less commercially profitable.  Addressing NTDs often also requires significant investment in local infrastructure such as access to clean water, healthy food, sanitation, mosquito netting, work safety conditions, health education and health care access. 

The World Health Organization (WHO) currently prioritizes 18 NTDs, affecting over 1 billion of the world’s poorest people.  A landmark study found that of more than 1,500 drugs that come to market between 1975 and 2004, only 10 were targeted at NTDs.  Approximately 1.4 billion people are currently affected by NTDs. 

What is Epidemiology?

Epidemiology is the science of tracking the pattern and the occurrence of disease.  It is essential for planning effective prevention strategies, efficient use of health care resources, and appropriate training and deployment of health care professionals.

Prevention strategies typically include:  health education, food security, travel advisories, vaccinations, equipping health facilities with appropriate equipment and medications, and public health campaigns (e.g., hygiene strategies during cold and flu season).

Endemic, Epidemic, and Pandemic

The etymology (study of word origins) of these three terms can be helpful in remembering the difference between them.  All three share the Greek word demos meaning ‘people’.

Notifiable Diseases in Canada and the Years Notifiable: