Infectious diseases

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Chapter 41 Infectious diseases

ANTIBIOTIC PRESCRIBING

A large volume of antibiotic prescriptions originate from the emergency department. To be responsible in your use of antibiotics, utilise up-to-date antibiotic guidelines and the infectious diseases and/or microbiology services in your hospital.

Antibiotic recommendations in this book are largely based on Therapeutic guidelines.1

Don’t feel pressure to prescribe unnecessary antibiotics—most patients would prefer a thorough assessment and explanation of the medical condition, rather than an unnecessary antibiotic prescription.

Antibiotics are not harmless. They have side effects such as diarrhoea, allergic reactions and drug interactions, and they put pressure on antibiotic resistance in the community. We have already reached the era of untreatable multiresistant organisms and it is likely to get worse.

More often than not, there is sufficient time to discuss your antibiotic prescribing with a more senior emergency department clinician, the infectious diseases service or the hospital team that will be taking over care of your patient. Once an antibiotic is prescribed, it is rarely stopped, no matter how unnecessary it may be.

The antibiotic creed1

M Microbiology guides therapy wherever possible.
I Indications should be evidence-based.
N Narrowest spectrum required.
D Dosage appropriate to the site and type of infection.
M Minimise duration of therapy.
E Ensure monotherapy in most situations.

Remember:

SEPSIS

(See also ‘Septic shock’ in Chapter 11, ‘Shock’.)

Early aggressive resuscitation in the emergency department has been shown to improve outcome.3

MENINGOCOCCAL INFECTION

Invasive meningococcal disease is life-threatening. The course can be fulminant with patients deteriorating within hours of onset of symptoms.

Neisseria meningitidis is a gram negative diplococcus with many serotypes. Serotypes B and C cause disease in Australia. Serotype C is now on the Australian childhood immunisation schedule. There is no vaccination available for serotype B.

Transmission is via asymptomatic nasal carriage (~ 10% population). Age groups 0–4 years and 15–25 years are most commonly affected by invasive disease with a seasonal peak in winter–spring.

Invasive infection can manifest as meningitis or more commonly as septicaemia (also referred to as meningococcaemia). Meningococcal meningitis has a high mortality rate of around 7%, but the mortality rate is even higher for meningococcal septicaemia at around 19%.

FEVER

Usually the cause of fever is apparent from other symptoms and signs, allowing focused investigation and management. First-line investigations such as urine culture, blood culture and chest X-ray may reveal an otherwise unapparent infective source.

When there is no apparent cause, a broad differential needs to be considered. Detailed and considered history taking, meticulous examination and tailored investigations are warranted.

Causes of fever can vary according to:

Herpes meningo-encephalitis

This is focal herpes simplex virus (HSV) infection of the cerebral cortex, especially the temporal lobe. Clinically, more neurological changes/seizures than bacterial meningitis.

Meningism is also present.

Request HSV PCR to be performed on CSF.

Malaria

Fever in the overseas traveller is malaria until proven otherwise.

Four plasmodium species cause human malaria—falciparum, vivax, ovale and malariae.

Falciparum causes almost all deaths directly related to malaria and is responsible for several million deaths throughout the world each year.