Chapter 29: Baffling bacterial infections

INTRODUCTION

Bacterial infections can present diagnostic brain-teasers, and a high index of suspicion is needed to pinpoint the diagnosis. Many are rarely encountered, thus making diagnosis more difficult yet demanding vigilance and clinical flexibility.

The list includes:

• tuberculosis

• infective endocarditis

• syphilis

• septicaemia

• the zoonoses (e.g. brucellosis, Lyme disease)

• clostridial infections: tetanus, gas gangrene, puerperal infection, botulism, pseudomembranous colitis

• hidden suppuration: abscess, osteomyelitis

• mycoplasma infections: atypical pneumonia

• Chlamydia infections: psittacosis, non-specific arthritis, pelvic inflammatory disease, trachoma, atypical pneumonia

• legionnaire disease

• Hansen disease

Chlamydia and rickettsial organisms have been confirmed as being small bacterial organisms.

Tuberculosis

Tuberculosis (TB), caused by Mycobacterium tuberculosis, still has a worldwide distribution with a very high prevalence in Asian countries where 60–80% of children below the age of 14 years are affected.¹ This has special implication in Australia, where large numbers of Asian migrants are settling. The WHO estimates that one-third of the world’s population is infected by the tubercle bacillus. It remains a deadly disease with about 2 million people worldwide dying of TB every year and 8 million new cases a year.

TB can be a mimic of other diseases and a high level of suspicion is necessary to consider the diagnosis, especially if there are only extrapulmonary manifestations. There may be no symptoms or signs, even in advanced disease. Ideally patients should be referred early for specialist management.

• newborn and infants

• adults over 60 years

• patients with HIV/AIDS

• chronic disease, e.g. diabetes

• crowded or unsanitary living conditions

• people affected by alcohol and drugs

• immigrants and refugees from endemic countries (especially Indian sub-continent, Papua New guinea, South East Asia, Sub Sahara and South Africa)

Primary infection

The primary infection usually involves the lungs. Transmission is by droplet infection. The focus is usually subpleural in the upper to mid zones and is almost always accompanied by lymph node involvement.

Erythema nodosum may accompany the primary infection (see FIG. 29.1). Primary TB is symptomless in most cases although there may be a vague, ‘not feeling well’ illness associated with a cough. In most people this pulmonary focus heals but leaves some surviving tubercle bacilli, even if it becomes calcified (the Ghon focus).

Progressive primary tuberculosis