Why Do I Frequently Have Low-Grade Fevers?

In addition to the harm caused by high fever to the body, low-grade fever can also lead to various discomfort symptoms. When our body temperature exceeds the normal range but is below 38 degrees Celsius, it is considered low-grade fever. There are many reasons for low-grade fever. If it occurs frequently, it is recommended that patients visit a hospital for examination as it can be caused by various reasons such as tuberculous infection, chronic biliary infection, urinary tract infection, etc.

Causes and Common Diseases:

1. Infectious causes are the most common, accounting for approximately 40%. Among all infectious low-grade fevers, tuberculous infection is the most frequent. Tuberculous infection manifests as low-grade fever in the afternoon, possibly accompanied by symptoms such as cough, fatigue, and sweating during the night or after waking up. Long-term low-grade fever caused by chronic biliary infection, chronic pyelonephritis, chronic urinary tract infection, chronic pelvic inflammatory disease, chronic otitis media, chronic sinusitis, AIDS, subacute endocarditis, and cytomegalovirus infection is also common.

2. Non-infectious causes include hyperthyroidism, rheumatic fever, lupus erythematosus, hematological diseases, tumors, and drug-induced fever.

3. Functional causes include physiological fever, seasonal fever, environmental fever, and neurofunctional fever. Except for environmental fever, it is more common in young women and children under 3 years old. The fever is mainly present in the morning and may be accompanied by symptoms such as sweating, hand tremors, insomnia, fatigue, and anorexia.

Differential Diagnosis:

1. Long-term low-grade fever is most commonly caused by tuberculous infection. Tuberculosis is relatively common in children. Besides low-grade fever, children may also experience changes in personality, such as becoming lethargic and inactive if they were previously active or becoming irritable and losing their appetite if they were previously calm. Therefore, tuberculin tests (OT) or triple skin tests (PPD-PHA) should be performed. Positive results can be used as a reference, but positive reactions can also be observed after children receive BCG vaccination. Additionally, a history of tuberculosis can also lead to positive reactions. Further examination of the erythrocyte sedimentation rate (ESR) is necessary. Typically, the ESR increases during active tuberculosis. Finally, X-ray examination of the lungs should be performed to detect any tuberculous lesions. If all the above tests are negative, tuberculosis can be ruled out.

2. Long-term low-grade fever can also be caused by viral infections, mainly affecting infants and young children, particularly throat infections without systemic manifestations. General examinations usually reveal no significant abnormalities or respiratory symptoms. This type of fever often persists for a long time after a high fever caused by a viral infection.

3. Bacterial infections can also lead to long-term low-grade fever in older children, such as streptococcal or Staphylococcus aureus infections in the throat. Throat secretion cultures can be performed to confirm the presence of bacteria. If streptococcal infection is detected, blood tests for anti-streptolysin O (ASO) can be performed. High titers indicate a history of streptococcal infection. Elevated anti-"O" levels may also suggest rheumatic fever, and it is important to assess for symptoms such as joint pain or swelling, the presence of erythematous rings (erythema migrans), and cardiac abnormalities, which are diagnostic criteria for rheumatic fever.