What are the causes of asymptomatic fever

Fever can be said to be the most common illness in life. You need medicine to cure a cold, you will have a fever if you catch a chill, you will have a fever if you have heatstroke, and there are many other situations that can cause fever. There are many reasons for fever, and the fever process is also very uncomfortable. Once you have a fever, you will lose energy and feel dizzy when walking, let alone work or study. If there are no other symptoms when you have a fever, it is difficult to determine the cause, so I would like to give you some knowledge in this regard.

There are many diseases that cause fever, which can be divided into two categories according to the different causes.

1. Infectious diseases

It includes various common pathogens, such as infectious diseases caused by bacteria, viruses, fungi, mycoplasma, etc. Among them, infectious fever caused by bacteria is the most common, followed by viruses, etc.

2. Non-infectious diseases

(1) Hematological diseases and malignant tumors: such as leukemia, malignant histiocytosis, malignant lymphoma, colon cancer, primary hepatocellular carcinoma, etc.

(2) Allergic diseases: such as drug fever and rheumatic fever.

(3) Connective tissue diseases: such as systemic lupus erythematosus (SIE), dermatomyositis, polyarteritis nodosa, mixed connective tissue disease (MCTD), etc.

(4) Others: such as hyperthyroidism and thyroid crisis. Severe dehydration or bleeding, heat stroke, heat stroke, fractures, extensive burns, cerebral hemorrhage, craniocerebral trauma, status epilepticus, heart failure, visceral vascular infarction, tissue necrosis, etc.

Differential Diagnosis

1. Infectious fever and non-infectious fever

1. Infectious fever often has the following characteristics

(1) Acute onset, with fever with or without chills.

(2) There are systemic and localized symptoms and signs.

(3) Blood picture: White blood cell count is higher than 1.2x109/L, or lower than 0.5x109/L.

(4) Nitrogen blue tetrazolium test (NBT): If the neutrophil reduction of NBT exceeds 20% (normal value <10%), it indicates bacterial infection, which helps to differentiate from viral infection and non-infectious fever. NBT may be false negative after the use of hormones.

(5) C-reactive protein (CRP) test: A positive result indicates bacterial infection and rheumatic fever, while a negative result usually indicates viral infection.

(6) Increased neutrophil alkaline phosphatase score: The normal value is 0-37. The higher the increase, the more favorable it is for the diagnosis of bacterial infection. It is more meaningful when excluding pregnancy, cancer, and malignant lymphoma. The use of hormones may cause it to increase or become false positive.

2. Non-infectious fever

Noninfectious fever has the following characteristics:

(1) The heat cycle is longer than 2 months. The longer the heat cycle, the greater the possibility.

(2) Long-term fever generally causes good symptoms, with no obvious symptoms of poisoning.

2. Common types of fever

1. Irregular heat

It means that the fever has no fixed pattern and the duration is also uncertain. It can be seen in various lung diseases and cardiopleurisy.

2. Generalized fever of unknown origin

Refers to all fevers of unknown cause. However, the narrow concept of fever is still used clinically, that is, fever of unknown cause. Fever persists for more than 3 weeks, with body temperature above 38.5℃, and a clear diagnosis cannot be made after detailed medical history, physical examination and routine laboratory tests.

3. Cancer fever

It refers to non-infectious fever directly related to cancer that occurs in cancer patients after infection has been ruled out and antibiotic treatment has been ineffective, as well as fever caused by treatment during the development of the tumor.

4. Qfever

A natural epidemic infectious disease caused by systemic infection of Coxiella burnetii, also known as Coxiella disease. Domestic animals such as cattle, sheep, dogs, horses, mules and pigs are the main sources of infection. The clinical features are fever, headache, and generalized muscle pain, but no rash, sometimes accompanied by interstitial pneumonia. A small number of patients develop chronic hepatitis or fatal endocarditis.

5. Infectious fever

Various infectious diseases such as bacteria, viruses, fungi, spirochetes, and malarial parasites act on the body temperature regulation center, the body temperature center dysfunction, or various reasons that cause excessive heat production and reduced heat dissipation, resulting in a temperature rise beyond the normal range.

6. Central fever

Refers to fever caused by abnormalities in the body temperature regulation center due to central nervous system lesions.

Remittent fever is also called septicemic fever. It means that the body temperature is continuously above 39 degrees, with large fluctuations. The temperature fluctuation range exceeds 2 degrees within 24 hours, but it is always above the normal level. It is common in sepsis, rheumatic fever, severe pulmonary tuberculosis and purulent inflammation. Persistent remittent fever may be seen in malignant granulomas.