Infection in an Immunocompromised Host

When the immune system doesn’t work as it should, even common germs can become serious threats. Understanding how to protect yourself when your body’s defenses are weakened is essential for staying healthy and safe.

Table of contents

• What Does It Mean to Be Immunocompromised?
• How the Immune System Protects You
• What Causes a Weakened Immune System
• Types of Infections and Their Risks
• Signs You May Have an Infection
• Why Infections Are More Dangerous
• How to Protect Yourself from Infections

What Does It Mean to Be Immunocompromised?

An immunocompromised host is a person who does not have the ability to respond normally to an infection because of an impaired or weakened immune system^[1]. This means your body’s natural defense system isn’t working as well as it should to fight off bacteria, viruses, fungi, and other germs that can make you sick^[2].

Being immunocompromised is also called having a weakened immune system. You might hear doctors use the term “immunosuppression” when this condition is caused by certain treatments or illnesses that you weren’t born with^[4].

Close to 7 million people in the United States have immune systems that don’t work well or at all, although the number could be even higher^[5]. Some people have a weakened immune system for just a limited time, while others live with this situation on a long-term or permanent basis.

How the Immune System Protects You

Your immune system is a complex network of organs, tissues, and cells that work together to protect you from infections. These body parts identify invaders like bacteria and viruses, then produce antibodies to attack these foreign substances entering your body^[13].

The immune system has two main parts that work together^[1]:

• Innate immunity provides rapid responses (within minutes to hours) using cells like neutrophils and macrophages that recognize broad classes of germs. This system doesn’t improve with repeated exposure to germs.
• Adaptive immunity is slower (taking days) but very specific, using B and T lymphocytes to recognize and remember individual germs. This system improves with repeated exposure to the same germ.

Host defense from infection also depends on physical barriers like your skin, stomach acid, and the mucus lining of your airways. These work together with your immune system to keep you healthy^[1].

What Causes a Weakened Immune System

Diseases, the side effects of certain medications, and receiving an organ or stem cell transplant are the most common causes of a compromised immune system^[4]. This inability to fight infection can be caused by a number of conditions, including diseases, malnutrition, and drugs^[2].

Conditions Present from Birth

Some people are born with conditions that affect their immune system. These congenital conditions include^[2]:

• Genetic syndromes
• B-cell defects
• Combined B-cell and T-cell defects
• T-cell defects
• Phagocyte deficiency or dysfunction
• Complement deficiencies

Acquired Conditions

Many health conditions can weaken your immune system over time. Diseases that can cause immunosuppression include^[4]:

• HIV (human immunodeficiency virus)
• Cancer, especially leukemia, lymphoma, and multiple myeloma
• Diabetes
• Autoimmune diseases
• Sickle cell disease
• Liver cirrhosis
• Viral hepatitis

Medical Treatments

Certain medical treatments can temporarily or permanently weaken your immune system. People who have a weakened immune system for a limited time include those who^[5]:

• Receive chemotherapy, immunotherapy, or radiation for diseases like cancer
• Take medications like steroids for a long period
• Have severe burns covering a large part of the body
• Are malnourished
• Had a bone marrow transplant

People who have a long-term weakened immune system include those who have no spleen, had an organ transplant, are older, or are very young, especially babies born too early^[5].

Types of Infections and Their Risks

Immunocompromised patients are susceptible to bacterial, fungal, viral, and parasitic infections that healthy immune systems usually overcome. They are also more susceptible to complications from common infections^[2].

Because each functional compartment of the immune system plays a specialized role in host defense, defects in specific functions lead to increased susceptibility to specific pathogens^[1]. The type of infections you’re most likely to get depends on what part of your immune system isn’t working properly.

B-Cell Defects

B-cell defects predispose patients to frequent sinus, lung, and respiratory tract infections. These patients are also vulnerable to infections with nonenveloped viruses, parvovirus B19, and rotavirus^[2].

Combined B-Cell and T-Cell Defects

Almost any organism can cause infection in patients with combined B-cell and T-cell defects. These patients often present with failure to thrive, thrush, and Pneumocystis jirovecii infection^[2]. Other commonly seen pathogens include:

• Streptococcus pneumoniae
• Pseudomonas aeruginosa
• Legionella pneumophila
• Listeria monocytogenes
• Mycobacterium species
• Fungi
• Herpesviruses (varicella-zoster virus, herpes simplex virus, cytomegalovirus, Epstein-Barr virus)
• Toxoplasma species
• Cryptosporidia
• Strongyloides species

T-Cell Defects

T-cell defects predispose to infections with Candida species, Mycobacterium avium-intracellulare complex, herpesviruses, and P jirovecii^[2].

Phagocyte Deficiency or Dysfunction

Phagocyte deficiency or dysfunction predisposes patients to infections with Staphylococcus aureus, Nocardia species, P aeruginosa, Serratia species, streptococci, other enteric organisms, and Candida, Burkholderia, Aspergillus, and Chromobacterium species^[2].

Complement Deficiency

Complement deficiency is associated with recurrent sinus and lung infections and invasive infections due to encapsulated bacteria such as S pneumoniae, Haemophilus influenzae, and Neisseria meningitidis^[2].

Signs You May Have an Infection

Getting sick a lot or having unusually long-lasting infections are the most common signs of having a compromised immune system^[4]. However, on its own, getting sick frequently doesn’t mean your immune system isn’t working properly—the kind of illnesses you get matters.

Being immunocompromised can mean^[4]:

• You get illnesses most people fight off without getting sick
• Illnesses that mildly affect most people make you severely sick
• Illnesses linger or it takes a longer time to recover from being sick
• You’re more likely to develop complications than others—like getting pneumonia after having a respiratory virus
• You might be more likely to get sick again with certain viral infections you’ve had in the past
• You don’t develop antibodies after getting vaccinated

Sometimes the only symptom of an infection may be fever. The usual symptoms like redness and swelling at the infection site may be absent in patients with weak immune systems^[3].

Why Infections Are More Dangerous

Infections pose special dangers for people with weakened immune systems for several important reasons^[3].

The usual symptoms may be absent. Patients with weak immune systems may not show the classic signs of infection such as redness and swelling at the infection site. Sometimes the only symptom of an infection may be fever.

The infection may move quickly. In the absence of infection-fighting white blood cells, the infection may rapidly progress from fever alone to sepsis (a serious condition where the body starts attacking itself) and death. For this reason, patients with weak immune systems who have low white blood cell counts are asked to report if they have fever right away. These patients are often hospitalized if they get a fever, so they can receive treatment with intravenous antibiotics^[3].

Their systems may not respond quickly to infection. Patients with weak immune systems may have trouble clearing infections from their bodies. For example, a viral infection such as the flu may take longer to clear from a patient with a weak immune system compared to a person with a healthy immune system^[3].

Infections can cause a serious illness called sepsis. Instead of fighting the infection, the body starts to attack itself, the healthy cells and tissues. Sepsis can lead to severe sepsis and septic shock. Severe sepsis and septic shock can leave long-lasting health problems. They can even cause death^[5].

According to the Centers for Disease Control, people with weakened immune systems are at greater risk for severe infections. Recent data shows that patients using certain B-cell depleting drugs like rituximab can face particularly serious outcomes. In one case series, 4 out of 5 patients using rituximab who were diagnosed with certain viral infections affecting the brain died^[9].

How to Protect Yourself from Infections

Preventing infections is critical for people with weakened immune systems. These are the general principles of preventing infection in patients with weak immune systems^[3].

Practice Good Hand Hygiene

Many infections are spread from bacteria or viruses that we pick up on our hands when we touch people or objects around us. Cleaning hands often is the best way to prevent the spread of infection^[3]. You should wash your hands with soap and water for at least 20 seconds. Don’t forget to clean under your nails and between your fingers. If you don’t have water, use a waterless cleanser^[5].

Avoid Contact with Sick People

Even a common cold virus can make a patient with a weak immune system very sick^[3]. Try to minimize your time outside of your home and avoid contact with anyone that has symptoms of sickness^[15].

Get Vaccinated

Get all vaccinations recommended by your healthcare provider. This includes the routine ones, like for measles, mumps, and rubella (MMR) and others, like for the flu, COVID-19, and pneumonia^[5]. Care providers for patients with weak immune systems should also receive all recommended vaccinations, including influenza and pertussis vaccines^[3].

According to guidelines from the Infectious Diseases Society of America (IDSA), most immunocompromised patients should be vaccinated^[2]. One of the best things both patients and caregivers can do is be fully vaccinated^[17].

Food Safety

A weak immune system makes you vulnerable to food poisoning and can make it more serious if you get it. Foods to avoid include^[14]:

• Raw fish and sushi
• Uncooked or undercooked eggs
• Rare burgers and steaks
• Soft cheeses like brie and Camembert, as well as blue-veined cheeses
• Uncooked deli meats like bologna and turkey breast
• Self-serve buffets and salad bars

Wash any produce you plan to eat raw with running water. Peel fruits before you eat them. Use a brush to scrub hard-skinned items like potatoes and carrots. Don’t soak produce in the sink, which may harbor bacteria. Stay away from raw or lightly cooked sprouts, like alfalfa sprouts^[14].

Water Safety

Even chlorinated water and saltwater can contain bugs that cause illness. Never swallow water when you swim in a pool, lake, river, or ocean. Don’t drink from springs or private wells. Depending on water quality in your area, even tap water—and ice made with it—could be risky. It may be best to drink only bottled water, or use a filter^[14].

Pet Safety

Pet waste may carry parasites like Toxoplasma gondii or cryptosporidium that can infect anyone, but immunocompromised people are more likely to get seriously ill. Wear gloves to clean the litter box or cage, or ask someone else to do it. Afterward, wash your hands thoroughly. Stay away from reptiles, amphibians, and farm animals^[14].

Protect Against Bug Bites

Mosquitoes and ticks spread infections that can be serious for those with weak immune systems. Before heading outdoors, use bug repellent with effective ingredients like DEET or picaridin, wear protective clothing, and avoid wooded and brushy areas. Check pets and yourself for ticks on your return^[14].

Other Precautions

Clean any breaks in your skin (scrapes and cuts) right away with soap and water. Cover them with a bandage^[5]. Wear gardening gloves to guard against cuts and scrapes to your hands, which give bacteria a way to enter your body. In some cases, your doctor may recommend that you avoid contact with soil^[14].

Smoking itself weakens your immune system, raising your risks for many diseases and infections. Ask your doctor about the best ways to quit^[14].