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Immunity and infection prevention

Fighting a microbe

The main article (“Fighting a microbe”) explains the body’s usual fight against a microbe. This topic shows how that fight looks different in leukaemia and why even a fever on its own is taken so seriously.

Last updated: ~1 min read
Slightly red skin with few cells nearby.
Figure 1.During neutropenia, infection leaves few traces.

01Short answer

In a healthy person, redness, swelling, pus and pain come from immune cells gathering at the site of infection. When neutrophils are very low, these “signs of battle” are faint or absent: a chest infection may cause no cough, a skin infection no pus, a urine infection no symptoms. Often the only sign is a fever or simply feeling unwell. That is why fever during neutropenia is treated as an emergency, and antibiotics are started quickly, before the source is found.

02Simple explanation

Few neutrophils mean few visible signs.

Fever is sometimes the only signal.

Antibiotics start quickly.

03Scientific explanation

Febrile neutropenia: the NCI notes that fever during neutropenia can be the first sign of a serious infection and needs immediate assessment.

Source: in some cases no source of infection is found, but treatment still matters.

04What happens in the body?

Infection without pus

With few defenders, redness and pus are hardly visible.

A single signal

Fever, chills or simply “I feel unwell” are enough.

A warm light rising in the dark.
Figure 2.Fever can be the only signal.

Help

Antibiotics strengthen the weakened defence until neutrophils recover.

Capsules of light joining the defenders.
Figure 3.Antibiotics help the defence.

05The fight during neutropenia

Four steps.

Entry — A microbe passes a gap.1EntryA microbe passes a gap.
Few defenders — Few cells arrive.2Few defendersFew cells arrive.
Fever — The signal rises.3FeverThe signal rises.
Help — Seek help fast.4HelpSeek help fast.

06Usual versus neutropenic infection

SignDuring neutropenia
Redness, swellingFaint or absent
PusOften absent
Cough, phlegmMay be slight
FeverThe most reliable signal

07Key terms

Febrile neutropenia
Fever while neutrophils are low.
Inflammation
The body’s reaction to injury and infection.
Pus
A mix of dead cells and microbes.
Empirical antibiotic
An antibiotic started before the microbe is identified.
Source
Where the infection started.

08Key points

  • Signs are faint during neutropenia.
  • Fever is the key signal.
  • Chills and weakness matter too.
  • Antibiotics start quickly.
  • Do not mask signs with fever reducers.
  • Call at once.

09Frequently asked questions

I have no fever but feel very unwell.

That is also a reason to call; sometimes infection starts without fever.

Can I take paracetamol and wait?

Unless your team has told you otherwise, call first; the medicine can hide a fever.

Why are antibiotics given before the source is found?

Delay is dangerous; the search for the source happens alongside.

10Questions for your doctor

Take these questions to your appointment. The ones you save are collected on the “My questions” page and stay on this device only.

  1. I have no fever but feel very unwell.

  2. Can I take paracetamol and wait?

  3. Why are antibiotics given before the source is found?

My questions

12Sources

  1. National Cancer Institute (NCI). Infection and Neutropenia during Cancer Treatment
  2. MedlinePlus (U.S. National Library of Medicine). Fever
  3. MedlinePlus (U.S. National Library of Medicine). Bacterial Infections
  4. American Cancer Society. Infections in People with Cancer
  5. American Cancer Society. What Is Chronic Lymphocytic Leukemia?
  6. National Cancer Institute (NCI). NCI Dictionary of Cancer Terms: thymus
  7. National Cancer Institute (NCI). NCI Dictionary of Cancer Terms: innate immunity
  8. National Cancer Institute (NCI). NCI Dictionary of Cancer Terms: adaptive immunity
  9. National Cancer Institute (NCI). NCI Dictionary of Cancer Terms: lymphatic system
  10. National Cancer Institute (NCI). Myelodysplastic/Myeloproliferative Neoplasms Treatment (PDQ®) — Patient Version
Medical disclaimerThis information is for educational purposes only and does not replace medical advice.
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