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Understanding antibiotic resistance
Understanding antibiotic resistance

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4.1 Traditional approaches to infection diagnosis

Your family doctor often relies on empirical diagnosis to decide what kind of infection you have. This means that they use their clinical experience to diagnose the infection based on your symptoms.

  • Why might an empirical diagnosis lead to unnecessary antibiotics being prescribed?

  • Empirical diagnoses rely on symptoms to diagnose an infection. For example, a persistent cough and fever could be symptoms of a chest infection. However, infections can be bacterial, viral or fungal and an empirical diagnosis cannot determine the cause of the infection. Antibiotics will not treat infections caused by viruses or fungi, therefore a prescription for antibiotics would be unnecessary in these cases.

In many cases a family doctor will send a sample of the infection for laboratory diagnostic testing. In the next activity, you reflect on your personal experience of being treated for an infection.

Activity 5 Being prescribed antibiotics

Timing: Allow about 5 minutes

Think about a time when you, or someone you know, was prescribed antibiotics. Then answer the questions below, based on your experience.

  1. Did the doctor send a sample for testing?
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  1. How long did you have to wait for the results?
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Discussion

If your family doctor suspects that you have a bacterial infection, they will often send samples for traditional laboratory diagnostic tests. However, as you will see below, it can take up to a week to get the results of these tests. Meanwhile, you might be prescribed broad-spectrum antibiotics to try to treat the infection and prevent it from becoming worse.

Traditional laboratory diagnostic tests rely on culturing the bacteria for at least 36 hours to determine the type of infection and the drugs that it is susceptible to (see Video 4). This can delay the prescription of narrow-spectrum antibiotics that specifically target the infection.

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Transcript: Video 4 Culturing bacteria to test for antibiotic susceptibility.

INSTRUCTOR
When a bacterial culture grows to cover the entire surface of a plate, it is called a lawn. To grow good lawn, we can use a swab. We immerse a pre-sterilised swab in a broth culture and drain the excess liquid against the side. We make a streak down the centre of the plate and then rub the swab across the surface of the plate. First in one direction and then in another to ensure maximum coverage. After overnight incubation, the lawn is visible. Lawns can be used to test the sensitivity of the bacteria to different substances, such as antibiotics. Here, specially prepared paper discs impregnated with a known quantity of antibiotic are used. The discs are placed on the surface of the plate after inoculation. After overnight incubation, clear zones-- indicating inhibition of bacterial growth-- can be seen around some or all of the discs. In this example, we can see that the culture contains at least two populations of bacteria. One that forms small, yellowish colonies and is sensitive to the antibiotic. And one that forms larger white colonies and is not sensitive to the antibiotic. This technique is very useful for testing antibiotic sensitivity and resistance patterns of pathogens.
End transcript: Video 4 Culturing bacteria to test for antibiotic susceptibility.
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Video 4 Culturing bacteria to test for antibiotic susceptibility.
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While the results of a traditional laboratory diagnostic test are being processed, broad-spectrum antibiotics are often prescribed to try to treat the infection before diagnosis. In some cases, the treatment will be effective. However, if the infection is not caused by pathogenic bacteria, or if the infection-causing bacteria are resistant to the prescribed antibiotic, another prescription may be required.

Rapid diagnostic tests do not rely on culturing bacteria so they can reduce the time taken to diagnose the infection (Figure 10). This means that doctors can quickly prescribe a treatment that effectively and specifically targets the infection. This helps to reduce the unnecessary prescribing of broad-spectrum antibiotics.

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Figure 10 Empirical and traditional diagnoses can delay optimal treatment but rapid diagnostic tests allow optimum treatments to be prescribed more quickly (O’Neill, 2016).
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This figure consists of an infographic from the O’Neill Review on Antimicrobial Resistance (2016). It illustrates how empirical and traditional diagnoses can delay optimal treatment. At the top of the figure the sick patient visits the doctor who performs an empirical diagnosis (purple) or orders a traditional (purple) or rapid diagnostic test (in blue). For an empirical diagnosis optimal treatment may never be achieved and may require a second empirical prescription or diagnostic tests. Traditional diagnostic tests may mean optimal treatment is delayed. Rapid diagnostic tests will mean that optimal treatment is reached quickly. The length of the arrow indicates the amount of time to reach optimal treatment.

Figure 10 Empirical and traditional diagnoses can delay optimal treatment but rapid diagnostic tests allow optimum treatments to be ...

In the next section, you will look at rapid diagnostic tests for infection more closely.