A system for the infectious diseases examination

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Chapter 16 A system for the infectious diseases examination

As it takes two to make a quarrel, so it takes two to make a disease, the microbe and its host.

Charles Chaplain (1856–1941)

We have selected two important presentations to be covered in this chapter to show how infectious diseases can be approached in a systematic manner.

Pyrexia of unknown origin (PUO)

This condition is defined as documented fever (>38 °C) of more than 3 weeks’ duration, where no cause is found despite basic investigations.1,2 The most frequent causes to consider are tuberculosis, occult abscess (usually intra-abdominal), osteomyelitis, infective endocarditis, lymphoma or leukaemia, systemic-onset juvenile rheumatoid arthritis, giant cell arteritis and drug fever (drug fever is responsible for 10% of fevers leading to hospital admission3). In studies of fever of unknown origin, infection is found to be the cause in 30%, neoplasia in 30%, connective tissue disease in 15% and miscellaneous causes in 15%; in 10% the aetiology remains unknown (Table 16.1). Remember, the longer the duration of the fever, the less likely there is an infectious aetiology. The majority of patients do not have a rare disease but rather a relatively common disease presenting in an unusual way.4

TABLE 16.1 Common causes of pyrexia of unknown origin

1 Neoplasms

• Hodgkin’s and non-Hodgkin’s lymphoma, leukaemia, malignant histiocytosis
• Other tumours: hepatic, renal, lung, disseminated carcinoma, atrial myxoma

2 Infections

• Bacterial: e.g. tuberculosis, brucellosis and other bacteraemias, abscess formation (especially pelvic or abdominal), endocarditis, pericarditis, osteomyelitis, cholangitis, pyelonephritis, pelvic inflammatory disease, prostatitis, syphilis, Lyme disease, borreliasis, cat scratch disease, dental abscess
• Viral: e.g. infectious mononucleosis, cytomegalovirus infection, hepatitis B or C, human immunodeficiency virus (HIV) infection, Ross River virus
• Parasitic, rickettsial and others: e.g. malaria, Q fever, toxoplasmosis
• Fungal: e.g. histoplasmosis, cryptococcosis, blastomycosis
3 Connective tissue diseases

• Juvenile rheumatoid arthritis, systemic lupus erythematosus
• Vasculitis, e.g. giant cell arteritis, polyarteritis nodosa
4 Drug fever 5 Miscellaneous

Inflammatory bowel disease, alcoholic liver disease, granulomatous disease (e.g. sarcoid), multiple pulmonary emboli, thyroiditis, adrenal insufficiency, phaeochromocytoma, familial Mediterranean fever and other hereditary periodic fever syndromes, factitious fever
6 Uncertain

History

The history may give a number of clues in these puzzling cases. In some patients a careful history may give the diagnosis where expensive tests have failed. See Questions box 16.1.

Questions box 16.1

General questions to ask the patient with a fever

! denotes symptoms for the possible diagnosis of an urgent or dangerous problem.

1. How long have you had high temperatures?
2. Have you taken your own temperature? How high has it been?
3. Have you had shivers and shakes (rigors)?
4. Has anyone you know had a similar illness?
5. What medications are you taking?
6. Have you had any recent illnesses?
7. Have you had any recent operations or medical procedures?
8. Have you travelled recently? Where to?
9. Did you take anti-malarial prophylaxis and have the recommended vaccinations for your trip?
10. Have you any pets? Have they been sick lately?

The time course of the fever and any associated symptoms must be uncovered. Symptoms from the various body systems should be sought methodically.

Examples include:

1. The gastrointestinal system—diarrhoea, abdominal pain, recent abdominal surgery (inflammatory bowel disease, diverticular disease, cholangitis).
2. The cardiovascular system—heart murmurs, dental procedures (infective endocarditis), chest pain (pericarditis).
3. Rheumatology—joint symptoms, rashes.
4. Neurology—headache (meningitis, cerebral abscess).
5. Genitourinary system—history of renal disease or infection, dysuria.
6. Respiratory system—old tuberculosis (TB) or recent TB contact, chest symptoms.

Details of any recent overseas travel are important. Find out also about hobbies and exposure to pets. Occupational exposure may be important. Take a drug history. Find out if the patient is involved in behaviour posing a risk of HIV infection. Patients who are already in hospital may have infected cannulas or old cannula sites.

Fever due to bacteraemia (the presence of organisms in the bloodstream) is associated with a higher risk of mortality. It is present in up to 20% of hospital patients with fever.5 Certain clinical findings modestly increase the likelihood of the presence of bacteraemia (Good signs guide 16.1).

GOOD SIGNS GUIDE 16.1 Clinical findings and bacteraemia

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Risk factors Likelihood ratio if
Present Absent
Age > 50 1.4 0.3
Temperature >38.5 1.2 NS
Rigors 1.8 NS
Tachycardia 1.2 NS
Respiratory rate >20 NS NS
Hypotension 2.0 NS

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