Chemotherapy is a systemic medical treatment designed to target and destroy rapidly dividing cells, a characteristic of cancer. While effective against tumors, this approach affects healthy, fast-growing cells throughout the body, including those in the bone marrow and the lining of the urinary tract. A Urinary Tract Infection (UTI) occurs when bacteria, typically from the digestive tract, enter the urethra and multiply, usually in the bladder. Chemotherapy does not directly introduce the bacteria that cause a UTI, but it dramatically alters the body’s defenses and the integrity of the urinary system. This creates an environment where the body is less capable of preventing or fighting off a bacterial infection, making UTIs a common and serious complication during cancer treatment.
How Chemotherapy Compromises Immune Defenses
The primary way chemotherapy increases the risk of infection is through myelosuppression, the temporary reduction in bone marrow activity. Since the bone marrow produces all blood cells, this suppression leads to a decrease in white blood cells responsible for fighting infection. Specifically, the drop in neutrophils, a type of white blood cell, is known as neutropenia.
Neutrophils are the immune system’s first line of defense, rapidly mobilizing to engulf and destroy invading bacteria, including those that enter the urinary tract. When chemotherapy reduces the neutrophil count, the body loses this immediate bacterial combat ability. A person with severe neutropenia cannot mount an effective immune response against small bacterial invasions.
The period of highest risk is known as the nadir, typically occurring 7 to 14 days after a chemotherapy dose. During the nadir, the neutrophil count is at its lowest point, leaving the patient profoundly susceptible to infections like UTIs. Bacteria normally cleared quickly by the bladder’s defenses can multiply unchecked. These infections often progress rapidly and require immediate medical attention due to the compromised defense system.
Direct Drug Effects on the Urinary Tract
Beyond systemic immune suppression, certain chemotherapy drugs can cause localized damage to the urinary tract, creating a second pathway for infection. Specific agents, such as cyclophosphamide and ifosfamide, are toxic to the bladder lining. These drugs are metabolized by the liver, producing acrolein, a byproduct that is excreted in the urine.
Acrolein is a corrosive compound that accumulates in the bladder, irritating and damaging the urothelium, the protective mucosal layer. This chemical irritation can lead to hemorrhagic cystitis, characterized by inflammation, pain, and bleeding in the bladder. The damage creates breaks in the mucosal barrier that normally prevents bacteria from adhering to the tissue and causing infection.
The compromised tissue of the bladder wall becomes an easy target for opportunistic bacterial colonization. This localized damage means that even if the patient’s neutrophil count is adequate, the damaged physical barrier increases the vulnerability to infection. Healthcare teams manage this risk by administering protective agents, like Mesna, which bind to and neutralize acrolein in the urine.
Identifying UTI Symptoms in Immunocompromised Patients
Recognizing a UTI in a patient undergoing chemotherapy can be challenging because classic symptoms may be absent or masked by other side effects. In a healthy person, a UTI often presents with painful or burning urination (dysuria), frequent urge to urinate, or cloudy urine. However, in neutropenic patients, the body may not produce enough inflammatory cells to cause all these typical symptoms.
Fever may be the only sign of a serious infection, a condition referred to as febrile neutropenia. Even a low-grade fever, such as a single temperature of 101°F (38.3°C), must be treated as a medical emergency. Other subtle or atypical signs of a spreading infection can include confusion, profound fatigue, or a rapid heart rate.
Patients and caregivers should report any changes in urinary habits or general well-being immediately to their oncology team. A UTI in an immunocompromised person carries a high risk of progressing rapidly to sepsis, a life-threatening systemic infection. Prompt evaluation, usually involving blood and urine cultures, is necessary to quickly start broad-spectrum intravenous antibiotics.