Postinfectious Neutropenia - Diagnosis and Treatment

Introduction

Neutrophils are a type of white blood cell (leukocyte) that serve as the first line of defense for the immune system. Neutrophils aid the immune system in fighting infections and healing injuries. White blood cells account for one percent of all cells in the body. Neutrophils are the most common white blood cells, accounting for between 50 to 80% of all white blood cells in the body.

An absolute neutrophil count determines whether or not the body has enough neutrophils and whether the count is above or below a healthy range. To keep the body functioning normally, the number of neutrophils in the body must remain within a certain range. If the neutrophil count is too high or too low, it may cause conditions such as:

• Neutropenia is a condition in which the neutrophil count is too low, resulting in swelling and repeated infections. Neutropenia can be caused by cancer treatment, an autoimmune disease, or an infection.

• Neutrophilia, or neutrophilic leukocytosis, occurs when the neutrophil count is abnormally high, which is frequently caused by a bacterial infection. Immature neutrophils leave the bone marrow too soon to fight the infection and enter the bloodstream.

What Is Neutropenia?

Neutropenia is characterized by lower-than-normal neutrophil levels in the blood. A lack of neutrophils makes it difficult for the body to fight germs and prevent infections. Even bacteria that a healthy body normally tolerates (such as bacteria in the mouth and intestines) can make one sick in severe cases.

Neutropenia can be classified as mild, moderate, or severe based on the number of neutrophils in a blood sample. According to many standards, the lowest normal limit for adults is around 1,500-1,800 neutrophils per microliter of blood. The neutrophil number range is:

• Mild neutropenia: 1,000 to 1,500.

• Moderate neutropenia: 500 to 1,000.

• Severe neutropenia: Fewer than 500.

Neutropenia can also be acute (temporary or short-term) or chronic (long-term), congenital (inherited), or acquired (a condition that happens over time).

What Is Postinfectious Neutropenia?

Post-infectious neutropenia refers to neutropenia that occurs in association with a viral or bacterial infection. The most common cause of postinfectious neutropenia in children is viral infections. It may be caused by almost any viral infection, but it is most commonly seen following varicella, influenza, measles, rubella, hepatitis, Epstein-Barr virus infection, or HIV infection. Although most cases are self-limiting, neutropenia following the Epstein-Barr virus and HIV infection can sometimes last for months. HIV infection is also associated with neutropenia, and approximately 70 % of HIV patients are neutropenic during their illness. The HIV virus suppresses hematopoiesis and raises the risk of contracting other infections.

Bacterial infections, with notable exceptions such as Brucella, rickettsial, and mycobacterial infections, are rare causes of significant neutropenia. Furthermore, severe sepsis from nearly any pathogen can cause neutropenia; this is most common in infants and the elderly, is thought to be caused by exhaustion of marrow granulocyte reserves, and has a poor prognosis.

What Are the Symptoms of Postinfectious Neutropenia?

Neutropenia does not cause symptoms, but the infections that can occur from neutropenia can cause symptoms which include:

• Fever (febrile neutropenia).

• Fatigue.

• Sore throat (pharyngitis).

• Swollen lymph nodes.

• Chills.

• Cough.

• Difficulty breathing.

• Ulcers in the mouth and around the anus.

• Swelling, pain, and rash at an infection site.

• Diarrhea.

• Burning sensation with urination or other urinary symptoms like urgency and frequency.

How Is Postinfectious Neutropenia Diagnosed?

Neutropenia is usually suspected in patients with frequent, severe, or unusual infections. CBC (complete blood count) with differential is used for confirmation. The first priority is to determine whether or not an infection exists; as the infection can be subtle. A physical examination evaluates the most common primary sites of infection which include the mucosal surfaces such as the alimentary tract (gums, pharynx, anus); abdomen; lungs; urinary tract; venipuncture sites; skin and fingernails; and vascular catheters. If the neutropenia is acute or severe, the laboratory evaluation must be done as soon as possible.

Cultures are the foundation of assessment. All febrile patients undergo at least two sets of bacterial and fungal blood cultures. If an IV catheter is present, cultures are drawn from the catheter and a separate peripheral vein. Chronic or persistent drainage material is also cultured for bacteria, fungi, and atypical Mycobacteria. Mucosal ulcers are cultured for herpes virus and Candida. Skin lesions are biopsied for cytology and culture. Urinalysis and urine cultures are done for all patients. If diarrhea is present, the stool is tested for enteric bacterial pathogens and Clostridium difficile toxins. To rule out pulmonary infections, sputum cultures are obtained.

Imaging studies are beneficial. Every patient undergoes a chest X-ray, especially immunocompromised patients. If symptoms or signs of sinusitis (e.g., positional headache, upper tooth or maxillary pain, facial swelling, nasal discharge) are present, a CT of the paranasal sinuses may be helpful. A CT (computed tomography) scan of the abdomen is usually performed if symptoms (such as pain) or history (such as recent surgery) suggest an intra-abdominal infection.

How Is Postinfectious Neutropenia Treated?

Infections that are suspected must always be treated right away. If fever or hypotension is present, a serious infection is suspected, and empiric, high-dose, broad-spectrum antibiotics are administered intravenously. The regimen is chosen depending on the most likely infectious agent, the antimicrobial susceptibility of pathogens at that particular institution, and the potential toxicity of the regimen.

• Vancomycin is only used if gram-positive organisms resistant to other drugs are suspected due to the risk of creating resistant organisms.

• Even if bacteremia is suspected or documented, indwelling vascular catheters are usually left in place, but removal is considered if infections involve S. aureus, Bacillus, Corynebacterium, Candida, or another fungus or if blood cultures remain positive despite appropriate antibiotics. Infections caused by coagulase-negative staphylococci usually resolve on their own with antimicrobial therapy.

• In neutropenic patients, indwelling Foley catheters can also predispose to infections, and catheter change or removal should be considered for persistent urinary infections.

• Antibiotic therapy is adjusted based on the results of sensitivity tests if cultures are positive. If a patient improves within 72 hours, antibiotics are given for at least seven days or until no symptoms or signs of infection are present.

• When neutropenia is transient (as in the case of myelosuppressive chemotherapy), antibiotics are usually continued until the neutrophil count is more than 500/mcL (microliter); however, stopping antimicrobials can be considered in selected patients with persistent neutropenia, particularly those with symptoms and signs of inflammation that have resolved, if cultures remain negative.

Conclusion

Neutropenia is treatable, so most people have a positive outcome. If the neutrophil levels are low due to a recent infection, they will most likely return to normal once the body has recovered. It is critical to avoid infections and if they do occur, they must be treated as soon as possible. A healthcare provider must be consulted if an individual requires frequent check-ups to ensure that one remains infection-free or may require medications to help prevent infections.