Patterns of infection analyzed by science of medicine


Conpects Of Infection

Infection can involve any organ or system of the body and thus embraces all medical disciplines. In this chapter an introduction is given to the general aspects, epidemiology, diagnosis, prevention and treatment of infection as well as descriptions of individual infectious diseases. Infections involving specific organs or systems are described in the appropriate chapters.

Infection differs from other diseases in a number of aspects. The most important is that it is caused by living microorganisms which can usually be identified, thus establishing the aetiology early in the illness. Many of these organisms, including all bacteria, are sensitive to antibiotics and most infections are potentially curable, unlike many non-infectious diseases which are degenerative and frequently become chronic. Communicability is another factor which differentiates infections from non-infectious diseases. Transmission of pathogenic organisms to other people, directly or indirectly, may lead to an epidemic. Finally, many infections are preventable by hygienic measures, by vaccines or by the judicious use of drugs (chemoprophylaxis).

Pattern of infection in developed countries

In the 20th century there has been a dramatic fall in the diseases in developed incidence of communicable countries. This is due to factors such as immunisation, antimicrobial chemotherapy, improved nutrition, and better sanitation and housing. Infectious diseases which have decreased, and in some instances almost disappeared, include diphtheria, poliomyelitis and tetanus. Smallpox, a lethal virus infection, has been eradicated from the world while another lethal infection, human immunodeficiency virus (HIV) infection, has emerged.

The pattern of infection in developed countries during the past two decades has been influenced by a number of factors (see the information box). These include the development of microbial resistance, immunosuppression, foreign travel, altered sexual behaviour, drug addiction, changes in animal husbandry and food production, and the availability and uptake of vaccines. Certain infections which had decreased or come under control are again emerging (resurgent infections), e.g. tuberculosis. In addition, the identification of microorganisms causing previously described diseases has opened up new therapeutic avenues; for example, the demonstration of the aetiological role of Helicobacter pylori in peptic ulceration has revolutionised treatment of that condition.

  • Improved uptake of vaccines
  • New vaccines, e.g. Haemophilus influenzae type B and hepatitis A
Animal husbandry and preparation of food
  • Salmonella and Campylobacter infections originating in poultry and eggs
  • Escherichia coli type 0157 causing haemorrhagic colitis associated with beef
  • Listeria infections from soft cheeses
Microbial resistance
Increased resistance in common bacterial pathogens including Staphylococcus aureus (MRSA). Gram-negative bacilli, Streptococcus pneumoniae, vancomycin-resistant enterococci (VRE) and Mycobacterium tuberculosis
Sexual behaviour
Increase in HIV infection and other sexually transmitted diseases
International travel
  • Importation of malaria (in 1996 there were 2500 cases in the UK, 2117 cases in continental France and 1021 cases in Germany)
  • Legionnaires' disease from holiday hotels
  • HIV infection
Advances in the treatment of malignant disease and in organ transplantation leading to infections with opportunistic organisms
Resurgence of infections
  • Tuberculosis-world-wide, especially in association with HIV infection
  • Poliomyelitis in the Netherlands (in a religious sect refusing vaccines)
  • Streptococcal infections in the USA (including rheumatic fever)
  • Measles in the USA (mainly in immigrants in inner cities)
  • Diphtheria in the former Soviet Union
  • Hepatitis A and typhoid fever in the former Yugoslavia
Intravenous drug addiction
Patterns of infection in tropical countries

In less developed countries, however, especially in the tropics, infection continues to be one of the most common causes of disease and death, particularly in children, and determines the strength of the working man, the health of the mother and the pattern of systemic disease in the community, including neoplasia. Multiple disease entities are the rule and the clinical patterns of illness differ in many ways from those in temperate zones. The complex interaction between chronic parasitism, respiratory and diarrhoeal diseases, tuberculosis, malnutrition and its immunosuppressive effects, and HIV infection, poses special problems for the health of children. Up to 40% of children may die before they reach 5 years of age in such undeveloped countries.

Chronic infections do serious damage to important organs, such as liver and kidneys in schistosomiasis, the heart in trypanosomiasis cruzi, the lungs, bones and lymph nodes in tuberculosis, the bone marrow reserves in malaria and hookworm infections, the gut in tropical sprue and the nerves in leprosy. These organs may then fail if the demand upon them is increased through work, growth, pregnancy or additional disease. Such diseases impose chronic ill health on millions of children and adults in the tropics.

Many of the decimating diseases of the past are controllable by vaccination (yellow fever), vector control (malaria and sleeping sickness) and general improvement in living standards (plague and relapsing fever), but control is imperfect and the diseases reappear. Other epidemic diseases such as cholera in Asia and meningococcal meningitis in Africa remain largely uncontrolled, and kill hundreds of thousands of people annually. Efficient vaccines exist for many diseases such as poliomyelitis, measles, rubella, meningitis and tetanus, but in many countries they have made little impact because of cost and the practical difficulty in delivering them.

Development, especially in the form of dams and irrigation, has often encouraged the spread of vector-borne disease such as malaria and schistosomiasis, while the exploitation of the Amazonian forests has resulted in mutilating outbreaks of mucocutaneous leishmaniasis. Migration to urban slums increases the risk of gastrointestinal disease and tuberculosis and of Western' diseases such as hypertension and has contributed materially to the AIDS epidemic which is wreaking havoc in developing countries, especially in Africa, the Indian subcontinent and South-east Asia.

Finally, in developing countries infectious diseases are frequently associated with natural disasters such as drought flooding and earthquakes as well as with war and revolution.

The information box illustrates patterns of infection i tropical countries.

Concepts of infection
Major manifestations of infection
Principles of management of infection
Diseases due to viruses
DNA viruses
Diseases due to chlamydiae
Diseases due to rickettsiae
Diseases due to bacteria
  • Streptococcal infections
  • Staphylococcal infections
  • Corynebacterial infections
  • Bacillus infections
  • Bordetella infections
  • Salmonella infections
  • Food poisoning
  • Dysentery
  • Other true bacterial infections
  • Mycobacterial infections
Diseases due to spirochaetes
  • Leptospira infections
  • Borrelia infections
  • Treponema infections
Diseases due to fungi (mycoses)
  • Cutaneous fungal infections
  • Subcutaneous fungal infections
  • Systemic fungal infections
Diseases due to protozoa
Diseases due to helminths
  • Trematode (fluke) infections
  • Cestode (tapeworm) infections
  • Nematode (roundworm) infections
  • Zoonotic helminth infections
Diseases due to arthropods
Sexually transmitted diseases
  • Sexually transmitted bacterial diseases
  • Sexually transmitted viral diseases
  • Miscellaneous conditions