Particular attention should be paid to the following:
1 Age of the patient
2 Foreign travel-remembering that certain diseases can exist both in the tropics and Europe, e.g. leishmaniasis, giardiasis
3 Immigrants-country of origin
4 Food and water-food poisoning is extremely common
5 Occupation, e.g.
(a) Sheep farmers-hydatid disease
(b) Sewer workers -leptospirosis
(c) Leather workers-anthrax
6 Domestic pets, e.g.
(c) Dogs- Toxocara canis infection, rabies
7 Sexual activity-hepatitis B, mixed enteric infections and HIV should be particularly considered in male homosexuals
8 Drug addiction-consider hepatitis Band C, HIV and pyogenic infections, e.g. staphylococcal
9 Tattooing-consider hepatitis B and C, HIV
10 Injections and transfusions-may act as a route of transmission for infections
11 Immunization history, e.g. BeG
A general examination should be performed with particular attention to skin rashes, lymphadenopathy and hepatosplenomegaly. In cases of sexually transmitted diseases the perineum, rectum and vagina should be inspected. The presence of a fever is helpful, but less emphasis is now placed on fever patterns because of improved laboratory diagnosis. High swinging fevers are characteristically seen with localized pus.
Tests should be performed as appropriate. If the diagnosis is obvious, e.g. a measles rash is present, no tests are necessary. The list below gives examples of situations in which tests are useful.
1 Full blood count and film are usually performed and often give a guide to the type of infection, although the changes are not invariable:
(a) Polymorphonuclear leucocytosis- bacterial infections
(b) Neutropenia – viral infections, brucellosis, typhoid, overwhelming septicaemia
(c) Lymphocytosis-viral infections, whooping cough
(d) Atypical lymphocytes-infectious mononucleosis
(e) Eosinophilia-parasitic infections, helminths
The erythrocyte sedimentation rate (ESR) and Creactive protein are usually raised.
2 Liver biochemistry is often slightly abnormal In
infections but this is a non-specific sign. The serum transferases are also raised in hepatitis and other liver infections.
4 Chest X-ray } These should also be performed, even in the absence of symptoms and signs
Further investigations specific diagnosis:
1 Blood culture.
2 Microscopic examination and culture of appropriate body fluids, e.g. urine, faeces, eSF, sputum.
3 Viruses can be identified in the above body fluids by:
(a) Electron microscopy.
(b) Tissue culture (cytomegalovirus).
(c) Immunological antigen capture techniques (rotavirus).
4 Immunodiagnosis-immunological techniques are now available for the identification of:
(a) Pathogen-specific antigens which can be detected in body fluids using polyvalent antisera or monoclonal antibodies .
(b) Specific serological responses to infection using immunodiffusion, complement fixation, indirect haemagglutination, indirect immunofluorescence or enzyme-linked immunosorbent assay (ELISA).
A high titre of IgM specific to a pathogen (e.g. hepatitis A or B virus, cytomegalovirus) is diagnostic of a recent infection. In infection a single raised IgG is unhelpful as this only indicates a previous rather than a current infection.
However, a rising titre can confirm the diagnosis (e.g. in brucellosis or Mycoplasma infection). These immunological techniques are particularly useful in the identification of pathogens that are difficult to culture by standard microbiological techniques or intracellular pathogens that require tissue culture.
S Tissue diagnosis-biopsy/aspiration with isolation of pathogen:
(a) Bone marrow/liver biopsy for generalized infections such as tuberculosis, leishmaniasis.
(b) Rarely, if the above technique is negative, splenic aspiration for leishmaniasis.
(c) Transbronchial biopsy for Pneumocystis carinii.
6 DNA/RNA-based techniques. Many genes encoding virulence factors and other specific proteins of pathogenic microorganisms have been cloned and sequenced. From this information DNA probes have been constructed and used for the detection of pathogen- specific DNA in body fluids or tissue. The use of amplification techniques like the polymerase chain reaction has increased the sensitivity of this approach which has already been introduced into practice.
7 Imaging procedures-ultrasound and CT scan (with needle aspiration) for abscesses in liver, lung, brain or abdomen.