Bacterial infections
Bacteria are the most common cause of infection during leukemia treatment. Many of them live on our skin, in the mouth and in the gut, and when immunity is weak they can get into the blood. This topic explains where bacterial infections start, how they are recognised, how antibiotics are chosen and what you can do to protect yourself from resistant bacteria.
01Short answer
02Simple explanation
Bacteria are single-celled living things too small to see. They can multiply on their own and can live in any part of the body. In a healthy person most bacteria are harmless, and some are even helpful.
In leukemia and after chemotherapy, when neutrophils are low, ordinary bacteria from the skin, mouth and gut can get into the blood. Having bacteria in the blood is called bacteremia. It is a serious condition that needs urgent treatment.
The first, and sometimes only, sign of a bacterial infection is a fever. There may also be chills (especially after the catheter is flushed), a cough, burning when passing urine, diarrhea, red and painful skin, or pain around the back passage.
Bacterial infections are treated with antibiotics. Doctors start an antibiotic against the most likely bacteria before they know exactly which one is to blame, and then adjust treatment when the laboratory results come back.
When antibiotics are used without need or in the wrong way, bacteria “get used to” them; this is called resistance. Taking antibiotics exactly as your doctor prescribes protects both you and other people.
03Scientific explanation
Gram-positive and gram-negative bacteria. In the laboratory, bacteria are stained using the Gram method and divided into two large groups by the structure of their wall. Gram-positive bacteria include staphylococci (from the skin, often linked to catheters), streptococci (from the mouth during mucositis) and enterococci. Gram-negative bacteria, such as E. coli, Klebsiella and Pseudomonas aeruginosa, come mainly from the gut and can cause severe sepsis very quickly. This is why the first antibiotic always covers gram-negative bacteria, including Pseudomonas.
First treatment. Under NICE and ESMO guidance, when neutropenic sepsis is suspected, an empirical intravenous antibiotic should start as soon as possible after arrival at hospital, ideally within one hour. The European ECIL-4 guidelines advise choosing the antibiotic according to local resistance patterns and the patient’s risk factors: “escalation” (start narrower and broaden if needed) for patients without particular risks, and “de-escalation” (start broad, then narrow) for those previously colonised with resistant bacteria, with a complicated presentation, or in centres where resistance is common. Treatment is reviewed after 72–96 hours according to the clinical course and microbiology results.
Prevention. Under ASCO/IDSA guidance, a preventive antibiotic (usually a fluoroquinolone) is recommended for high-risk patients whose neutrophils are expected to stay below 0.1×10⁹/L for more than 7 days. In a randomised trial published in the NEJM in 2005, fever during neutropenia occurred in 65% of patients taking levofloxacin and in 85% of those taking placebo; bloodstream infections were also reduced, while death rates were similar in the two groups. The downside of prevention is the risk of more resistance, so the decision is made individually.
Resistant bacteria and C. diff. MRSA (methicillin-resistant Staphylococcus aureus), vancomycin-resistant enterococci, and gram-negative bacteria that produce extended-spectrum beta-lactamases (ESBL) or carbapenemases make treatment harder. According to WHO, bacterial resistance was associated with more than 4.7 million deaths worldwide in 2021. Some hospitals take screening swabs on admission. Antibiotics also change the normal gut flora, which can open the way to Clostridioides difficile infection: according to the CDC, the risk of this infection is up to 10 times higher while taking an antibiotic and in the month afterwards.
04What happens in the body?
When should you seek urgent help?
Call the 24-hour number or emergency services straight away if your temperature is 38 °C or higher (or reaches the threshold your team gave you), if you start shivering, especially during or after a catheter flush, or if you have breathlessness, confusion, passing less urine, severe abdominal pain or bloody diarrhea. Do not start antibiotics you have at home on your own; this can spoil the blood culture result.
Where do the bacteria come from?
Many bacterial infections start with the person’s own bacteria: skin bacteria enter through catheter and needle sites, mouth bacteria through mucositis sores, and gut bacteria through a damaged gut wall. Resistant bacteria can also be passed on in hospital and by unwashed hands. Hand hygiene, mouth care and proper catheter care narrow these routes.
What happens in hospital?
The doctor examines you, takes blood cultures and other samples, and starts an intravenous antibiotic without delay. Culture results can take several days; if a bacterium is found, the most suitable antibiotic is chosen. With a catheter infection, the catheter sometimes has to be removed. How long treatment lasts depends on where the infection is, the type of bacterium and the recovery of neutrophils.
How to take antibiotics correctly
Take the antibiotic exactly as prescribed, keeping to the times and the length of the course. Do not stop without talking to your doctor, even if you feel well. Do not keep leftover antibiotics or give them to others. Tell your team exactly which antibiotic you reacted to in the past and how; an accurate “allergy” record makes the choice easier.
Diarrhea during antibiotics
Antibiotics can change the gut flora. If you have watery stools several times a day, abdominal pain or a fever, tell your team: they may test for C. diff. Do not take anti-diarrhea medicines without talking to your doctor. Drink plenty of fluids and wash your hands with soap after using the toilet, as alcohol hand rub does not work well against C. diff spores.
Questions you can ask your doctor
Do I need a preventive antibiotic, and for how long? Which signs mean I should come in straight away? What did the blood culture show, and will the antibiotic change because of it? Might my catheter need to be removed? Have I been found to carry a resistant bacterium, and what does that change in daily life? When will the antibiotic course end?
05When a bacterial infection is suspected
The usual steps when a fever appears during neutropenia (simplified).
06Common bacterial infections (simplified)
| Where? | Possible signs | Common bacteria |
|---|---|---|
| Blood (bacteremia) | Fever, chills, weakness, falling blood pressure | Skin and gut bacteria |
| Catheter | Redness, pain, discharge; chills after flushing | Staphylococci |
| Lungs | Cough, breathlessness, chest pain | Pneumococcus, Pseudomonas and others |
| Urinary tract | Burning, passing urine often, cloudy urine | E. coli and other gut bacteria |
| Skin and around the anus | Redness, swelling, pain | Staphylococci, streptococci, gut bacteria |
| Gut | Watery diarrhea, abdominal pain, fever | Clostridioides difficile and others |
* During neutropenia these signs may be faint or absent; a fever is often the only signal. Your hematology team makes the diagnosis.
07Key terms
- Bacterium
- A single-celled germ; some cause infections.
- Bacteremia
- Bacteria in the blood.
- Gram stain
- A laboratory method that sorts bacteria into gram-positive and gram-negative groups.
- Antibiotic
- A medicine that kills bacteria or stops them multiplying.
- Broad-spectrum antibiotic
- An antibiotic that works against many kinds of bacteria.
- Sensitivity test
- A test showing which antibiotics a bacterium responds to.
- Preventive antibiotic
- An antibiotic given in advance to prevent infection.
- Resistance
- A bacterium no longer responding to an antibiotic.
- MRSA
- Staphylococcus aureus that is resistant to many antibiotics.
- C. diff
- A bacterium that can cause diarrhea and gut inflammation after antibiotics.
08Key points
- Bacteria are the most common cause of infection during treatment.
- The source is often our own skin, mouth and gut bacteria.
- A fever is often the first and only sign.
- Antibiotics start as soon as possible, without waiting for results.
- Treatment is fine-tuned when results come back.
- Preventive antibiotics are used only in certain risk groups.
- Take antibiotics only as prescribed.
- Tell your team about watery diarrhea during antibiotics.
09Frequently asked questions
Why am I given several antibiotics at once?
Sometimes first treatment is kept broad to cover different bacteria, or because a resistant bacterium is suspected. When results arrive, doctors often simplify treatment. This approach follows international guidelines.
I take a preventive antibiotic. Can I still get a fever?
Yes. Prevention lowers the risk but does not remove it. If you get a fever while taking a preventive antibiotic, you still need to call straight away.
My blood culture was negative, so why are the antibiotics continuing?
Bacteria are not always found. Your doctor decides when to stop based on your condition, your neutrophil level and how the fever behaves. In some stable patients, guidelines allow antibiotics to be stopped earlier.
A resistant bacterium was found. Does that mean it cannot be treated?
No. A resistant bacterium does not respond to some antibiotics, but other medicines usually work. The hospital may use extra hygiene measures to protect you and others.
I am allergic to penicillin. Does this make treatment harder?
Allergy information matters, but doctors always find an alternative. Say exactly what reaction you had: a rash, difficulty breathing or an upset stomach mean different things.
Do probiotics prevent diarrhea from antibiotics?
During neutropenia, supplements containing live germs can be dangerous, because those germs can themselves get into the blood. Take any probiotic or supplement only with your hematology team’s approval.
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.
Which bacterium was found, and which antibiotic is being given?
How long will the antibiotic course last?
What should we do if I am allergic to antibiotics?
What should I watch to help prevent bacterial infection?
12Sources
- MedlinePlus (U.S. National Library of Medicine). Bacterial Infections
- MedlinePlus (U.S. National Library of Medicine). Antibiotic Resistance
- National Cancer Institute (NCI). Infection and Neutropenia during Cancer Treatment
- American Cancer Society. Infections in People with Cancer
- Centers for Disease Control and Prevention (CDC). Healthy Habits: Antibiotic Do’s and Don’ts
- Centers for Disease Control and Prevention (CDC). About C. diff
- Centers for Disease Control and Prevention (CDC). Methicillin-resistant Staphylococcus aureus (MRSA) Basics
- World Health Organization (WHO). Antimicrobial resistance (fact sheet)
- National Institute for Health and Care Excellence (NICE). Neutropenic sepsis: prevention and management in people with cancer (CG151)
- Journal of Clinical Oncology (ASCO and IDSA), 2018. Antimicrobial Prophylaxis for Adult Patients With Cancer-Related Immunosuppression: ASCO and IDSA Clinical Practice Guideline Update
- Clinical Infectious Diseases (IDSA), 2011. Clinical practice guideline for the use of antimicrobial agents in neutropenic patients with cancer: 2010 update by the Infectious Diseases Society of America
- Annals of Oncology (ESMO), 2016. Management of febrile neutropaenia: ESMO Clinical Practice Guidelines
- Haematologica (ECIL-4), 2013. European guidelines for empirical antibacterial therapy for febrile neutropenic patients in the era of growing resistance
- New England Journal of Medicine, 2005. Levofloxacin to prevent bacterial infection in patients with cancer and neutropenia