Neutrophils count in bacterial & viral infections

Although not applicable in all cases, neutrophils count in acute infection can be indicative of a bacterial or a viral infection. Note as I mentioned it’s not applicable in all cases and all patients. So use this as supportive finding along with other findings to come up to the conclusion while diagnosing a patient with viral or bacterial infection.


A state of high neutrophil level is known as neutrophilia. When the neutrophil count goes above 8000, it’s considered a high neutrophil level.

There can be many causes to the high neutrophil percentage in the complete blood count. Most common cause is the infection from bacteria or virus. Fungal and parasitic infections can lead to high neutrophil percentage too.

There can be non-infectious causes of high neutrophil count too.

Causes of neutrophilia

Following are common causes of high neutrophil percentage.

  • Infectious causes of neutrophilia
    • Bacteria
    • Viruses
    • Fungi
    • Parasites
  • Non-infectious causes of high neutrophilia
    • Inflammation
      • burn injuries
      • acute arthritis
    • Heart attack
    • Intestinal obstruction
    • Post-operative state
    • Rheumatic fever
    • Kidney failure or Severe glomerulonephritis
    • Hypersensitivity
  • Medicines
    • Corticosteroids
  • Others
    • Ketoacidosis
    • Anemia
    • Severe haemorrhage
    • Chronic leukaemia and other malignant tumors
    • Eclampsia (sudden muscle movements or convulsions during pregnancy)
    • Hereditary


Reduction in the quantity of neutrophils is called neutropenia.

Neutrophils count in bacterial and viral infections


There is a difference in neutrophils response to bacterial and viral infections. The difference is due to the characteristics of both. One tends to activate the increase in neutrophils count while the other one may in fact reduce it.

Neutrophils count in bacterial infections

The count of neutrophils increases in cases of bacterial infection. However, there are some exceptions like:

  • Typhoid
  • Brucellosis

What is Neutropenia

Neutropenia means low neutrophils count in the blood. As discussed above, typhoid and brucellosis can cause neutropenia.

Neutrophils count in viral infections

Certain viral infections tend to reduce the neutrophils count (e.g hepatitis (B), influenza, rubella, rubeola, and mumps), resulting in neutropenia.

So next time you face a patient with symptoms of an acute infection and a valid history, the neutrophils count would be helpful in determining which type of infection is going on in the patient, viral or bacterial. But do remember that some bacterial infection or other situations also lead to low neutrophils count.

Can Neutrophil can lower in Bacterial and elevate in Viral infections?

Yes it can. To understand this, first we have to see why white blood cells count increase or decrease in particular condition.

E.g., prior to current bacterial infection, if the patient already had any other infection, his WBC count would already be low, thus going further down below normal as too many WBCs have already been used and called for action. In fact this condition makes a person more susceptible to secondary infections, including bacterial, viral, etc.

It’s important to remember that BOTH bacteria and viruses can raise or lower the white blood cells count.

Note: This post is not at all an alternate to professional medical consultation, consult a doctor if you’re having any symptoms of viral or bacterial infection and don’t take only neutrophil count as the indicator of bacterial or viral infection.

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