Viral infection: Many viral infections can cause transient neutropenia and a decrease in the total white blood cell count. The age of the patient and the presentation make this a common and likely diagnosis.

Medication-induced neutropenia: Certain medications, such as antibiotics (e.g., trimethoprim-sulfamethoxazole), anticonvulsants, and some over-the-counter drugs, can cause neutropenia. Given the patient's age, it's possible they are taking medications for various reasons.
Benign ethnic neutropenia: This condition is more common in individuals of African or Middle Eastern descent and is characterized by a chronically low neutrophil count without an increased risk of infection. It's essential to consider the patient's ethnic background.
Autoimmune neutropenia: This condition can occur at any age and is characterized by the production of antibodies against neutrophils, leading to their destruction.

Aplastic anemia: A rare but serious condition where the bone marrow fails to produce blood cells. It can present with pancytopenia, including neutropenia, and is critical to diagnose early due to its potential severity and treatment options.
Leukemia or lymphoma: Although less common, these malignancies can present with abnormal blood cell counts, including neutropenia. Early diagnosis is crucial for effective treatment.
Severe combined immunodeficiency (SCID): A group of rare disorders caused by mutations in different genes involved in the development and function of the immune system. SCID can present with severe infections and abnormal blood cell counts.

Cyclic neutropenia: A rare genetic disorder characterized by periodic episodes of neutropenia, which can be severe and increase the risk of infections.
Shwachman-Diamond syndrome: A rare genetic disorder that affects the bone marrow, pancreas, and skeleton, leading to neutropenia, among other symptoms.
Kostmann syndrome: A rare congenital disorder characterized by severe neutropenia due to bone marrow failure, which increases the risk of severe infections.