Haematological infections are a serious concern for people whose blood and immune systems are compromised by diseases affecting blood cells or treatments that weaken the body’s natural defenses. Understanding how infections develop in these vulnerable patients, and how to reduce the risk of becoming ill, can make an important difference in health outcomes and quality of life.

What Are Haematological Infections?

Haematological infections refer to infections that occur in patients with blood disorders or diseases affecting the blood-forming organs, such as the bone marrow. These infections happen because the underlying blood condition or its treatment weakens the immune system, making it harder for the body to fight off bacteria, viruses, fungi, and other harmful organisms.^[3]

The blood system plays a crucial role in protecting the body from infection. White blood cells, which are part of the blood, help fight off germs and infections. When blood disorders or treatments like chemotherapy reduce the number or function of these white blood cells, patients become more vulnerable to infections that healthy people might easily fight off.^[1]

People with blood cancers, such as leukemia, lymphoma, or myeloma, as well as those undergoing treatments like stem cell transplants or chemotherapy, are particularly at risk. The relationship between blood health and infection is complex, involving not just white blood cells but also other blood components and proteins that help the body respond to germs.^[2]

Who Is Most at Risk?

Infections are not equally likely in all patients with blood disorders. The risk depends heavily on the specific blood condition, the type and intensity of treatment received, and how severely the immune system has been affected.^[3]

Patients with blood cancers face some of the highest infection risks. Those who have undergone allogeneic hematopoietic stem cell transplantation, a procedure where stem cells from a donor are transplanted into a patient, are especially vulnerable. This treatment significantly weakens the immune system, making infections a major cause of illness and death in these patients.^[3]

The level of immunosuppression, or how weakened the immune system is, largely determines what type of infections a patient might develop. Neutropenia, a condition where the number of neutrophils (a type of white blood cell) drops very low, makes patients susceptible to severe bacterial infections. When neutropenia lasts for a long time, patients also become vulnerable to fungal infections. Meanwhile, patients with reduced T-cell function, another component of the immune system, face increased risks from both fungal and viral infections.^[3]

Patients receiving chemotherapy for blood cancers often experience periods of severe neutropenia, during which even minor infections can become life-threatening emergencies. The duration and depth of neutropenia directly correlate with infection risk—the longer and more severe the neutropenia, the greater the danger.^[8]

Common Causes of Infections

The types of germs that cause infections in patients with blood disorders differ from those affecting healthy individuals. While healthy people typically fight off many organisms without issue, weakened immune systems cannot mount effective defenses, allowing infections to take hold and spread.^[3]

Bacterial infections are among the most common and dangerous. The widespread use of broad-spectrum antibacterial drugs, medications that work against many types of bacteria, has helped reduce death rates from bacterial infections during periods of severe neutropenia. However, a new challenge has emerged: the development of multiresistant strains of bacteria that don’t respond to standard antibiotics. In several countries, these resistant bacteria have become a major threat, creating urgent need for new antibacterial medications and better infection control strategies to prevent their spread.^[3]

Fungal infections pose serious risks, particularly for patients experiencing prolonged neutropenia or those who have received stem cell transplants. Early diagnosis through imaging tests and laboratory tests that detect fungal antigens or DNA is crucial for effective management. High-risk patients often receive preventive antifungal medications to reduce their chances of developing these dangerous infections.^[3]

Viral infections are particularly important in patients who have undergone allogeneic stem cell transplants, though they can affect other blood disorder patients as well. Early diagnosis, usually through tests that detect viral genetic material in blood or tissue samples, is key to proper management. For some viruses, especially herpesviruses (a family of viruses that includes chickenpox and cold sore viruses), preventive and treatment medications are available.^[3]

The body’s natural barriers also play a role in infection risk. Treatments for blood disorders can damage the lining of the mouth and digestive tract, creating entry points for bacteria that normally live harmlessly in the body. Medical devices like central venous catheters, which are tubes inserted into large veins to deliver medications and fluids, can also provide pathways for germs to enter the bloodstream.^[8]

Recognizing the Signs and Symptoms

Understanding the warning signs of infection is critical for patients with blood disorders and their caregivers. Because the immune system is compromised, typical signs of infection may be subtle or absent, making vigilance even more important.^[12]

Fever is often the first and most important warning sign. For patients undergoing treatment for blood cancers, febrile neutropenia, which means having a fever while experiencing very low white blood cell counts, is a medical emergency requiring immediate attention. Even without other symptoms, fever in a neutropenic patient demands urgent evaluation and typically immediate antibiotic treatment.^[3]

Other symptoms can include chills, unusual fatigue beyond what’s typical for the underlying condition, shortness of breath, cough, sore throat, painful urination, redness or swelling around wounds or catheter sites, and general feelings of being unwell. Because neutropenic patients cannot mount strong inflammatory responses, infections may not cause the redness, swelling, or pus formation that typically signal infection in healthy individuals.^[12]

The speed at which infections progress in immunocompromised patients makes early recognition vital. What might start as mild symptoms can escalate to severe, life-threatening illness within hours. This is why healthcare teams emphasize that patients and families should not wait to see if symptoms improve on their own but should seek medical attention immediately when concerning signs appear.^[12]

Prevention Strategies

Preventing infections in patients with blood disorders involves a two-pronged approach: infection control measures and antimicrobial medications given preventively. Both strategies have important roles, though each comes with considerations.^[6]

Infection control measures are safe practices aimed at reducing exposure to harmful germs. These include frequent and thorough handwashing, which is perhaps the single most important step anyone can take. Patients should wash hands with soap and warm water for at least 15 seconds, or use alcohol-based hand sanitizer containing at least 70% alcohol. Hand hygiene is especially crucial after using the bathroom, before eating, and after touching public surfaces like door handles or elevator buttons.^[17]

Avoiding contact with people who are sick is another key strategy. During high-risk periods, patients may need to limit visits from friends and family, and visitors should always wash hands before entering the patient’s room. Anyone with a cold, flu, cough, fever, or any sign of illness should not visit until they are fully recovered.^[17]

Environmental precautions can also help. Patients may be advised to avoid crowded places, wear protective masks in public settings, stay away from gardening and soil (which can harbor fungi), avoid live plants and flowers in hospital rooms, and steer clear of moldy environments. Food safety is equally important—patients should avoid undercooked meat and eggs, unpasteurized dairy products, and foods that might carry bacteria.^[9]

Antimicrobial prophylaxis, or preventive medication, is the practice of giving antibiotics, antifungals, or antiviral drugs before infection occurs. Studies have shown that fluoroquinolone antibiotics can reduce bacterial infections in high-risk patients. However, prophylactic antimicrobials come with drawbacks: they can contribute to antimicrobial resistance (where germs become immune to medications), cause side effects, and increase healthcare costs.^[6]

Healthcare providers carefully weigh the benefits and risks of antimicrobial prophylaxis for each patient. Factors considered include how high the person’s infection risk is, which germs are most common in their particular healthcare setting, how long the risk period will last, and the patient’s history with infections or drug reactions. The higher the infection risk and the shorter the at-risk period, the more likely prophylaxis will help.^[6]

How the Body Changes During Blood Disorders

Understanding what happens in the body during blood disorders and their treatment helps explain why infections become such serious threats. Blood disorders affect the production and function of blood cells, which normally protect against disease.^[2]

The bone marrow, the soft tissue inside bones, is where blood cells are made. In many blood disorders, the bone marrow either produces abnormal blood cells or stops producing enough healthy cells. This affects all types of blood cells: red blood cells that carry oxygen, white blood cells that fight infection, and platelets that help blood clot.^[5]

When white blood cell numbers drop or these cells don’t function properly, the body loses its primary defense against invading organisms. Neutrophils, the most abundant type of white blood cell, are usually the first responders to bacterial infections. Without adequate neutrophils, bacteria can multiply unchecked, spreading through the bloodstream and causing overwhelming infection.^[3]

Beyond the cells themselves, blood disorders can affect immune proteins and other defense mechanisms. Some blood disorders cause hypogammaglobulinemia, a condition where antibody levels in blood are too low. Antibodies are proteins that recognize and help destroy specific germs. Without sufficient antibodies, patients become susceptible to infections that antibodies would normally prevent.^[8]

The relationship between blood and immunity extends to other blood components as well. Research has revealed that red blood cells, platelets, and proteins involved in blood clotting also play roles in immune defense and the body’s response to infections. These newly understood functions represent complex interactions that evolved over time to help organisms survive infections, and disruptions in these systems can compromise infection resistance.^[2]

Chemotherapy and radiation therapy, common treatments for blood cancers, further impair immune function. These therapies kill rapidly dividing cells, which include cancer cells but also healthy bone marrow cells. The result is often severe, prolonged drops in white blood cell counts, leaving patients highly vulnerable during treatment cycles. Stem cell transplantation involves completely wiping out the patient’s existing bone marrow and immune system before rebuilding it, creating an extended period of profound immunosuppression.^[3]

Recovery of immune function after treatment varies widely. Some patients regain normal immunity relatively quickly, while others experience lasting immune deficits. Even patients in remission, whose cancer is no longer detectable, may remain at higher infection risk than the general population, particularly if they underwent intensive treatments or transplantation.^[9]