Symptoms:

Initial symptoms, similar to the common cold, usually develop about a week after exposure to the bacteria.

Severe episodes of coughing start about 10 to 12 days later. In children, the coughing often ends with a "whoop" noise. The sound is produced when the patient tries to take a breath. The whoop noise is rare in patients under 6 months of age and in adults.

Coughing spells may lead to vomiting or a short loss of consciousness. Pertussis should always be considered when vomiting occurs with coughing. In infants, choking spells are common.

Other pertussis symptoms include:

• Runny nose
• Slight fever (102 °F or lower)
• Diarrhea

Signs and tests:

The initial diagnosis is usually based on the symptoms. However, when the symptoms are not obvious, pertussis may be difficult to diagnose. In very young infants, the symptoms may be caused by pneumonia instead.

To know for sure, the health care provider may take a sample of mucus from the nasal secretions and send it to a lab, which tests it for pertussis. While this can offer an accurate diagnosis, the test takes some time, and treatment is usually started before the results are ready.

Some patients may have a complete blood count that shows large numbers of lymphocytes.