The Delaware Division of Public Health (DPH) is sending this health advisory to alert clinicians and health care partners about increased numbers of pertussis cases.

Summary

Clinicians and health care partners should be aware of the increased number of pertussis (whooping cough) cases in Delaware, with the increase being primarily among adolescents and infants, including cases that are up to date on vaccinations. The best way to prevent pertussis is through vaccination, although breakthrough cases can occasionally happen as the protection from the vaccine wanes. Illness is generally milder in vaccinated individuals. All infected individuals should receive antibiotic treatment, and post-exposure prophylaxis (PEP) with antibiotics is recommended for all household contacts, close contacts, and contacts who have a high risk of developing severe pertussis.

Background

Delaware has had low-level pertussis activity since the most recently identified outbreak in May 2024. A similar pattern is arising as of June 11, 2026, with a sudden increase in cases, primarily in adolescents and infants. Pertussis is a highly contagious bacterial disease caused by Bordetella pertussis. The incubation period is typically seven to 10 days but can range from five to 21 days. Individuals are infectious from the onset of symptoms until three weeks after onset of paroxysmal cough or until a complete course of a prescribed antibiotic. 

Early pertussis symptoms are typically indistinguishable from other upper respiratory disease, including runny nose, nasal congestion, and sometimes a mild fever. Cough onset is typically one to two weeks after the start of symptoms. The cough is initially mild but may progress to paroxysms, inspiratory whoop, difficulty breathing, and post-tussive vomiting. Severe coughing can last for months, even after treatment. Infants too young for vaccination are at the greatest risk for complications and death. Infants may present with apnea and skin color change from oxygen deprivation.

The best way to prevent pertussis is through vaccination, although breakthrough cases can occasionally happen as the protection from the vaccine wanes. Illness is generally milder in vaccinated individuals. 

Diagnostic testing

Pertussis should be considered in the differential diagnosis for patients who present with prolonged cough illness, regardless of immunization status. Nasopharyngeal samples should be sent for polymerase chain reaction (PCR) testing. Serology labs are not recommended early in illness. Guidance on sample collection may be found on the CDC website: https://www.cdc.gov/pertussis/php/laboratories/index.html.

Reporting

Pertussis is a reportable disease in Delaware. It is imperative that pertussis cases are reported in a timely manner because of the need for time-sensitive administration of postexposure prophylaxis (PEP) to those exposed. All confirmed or suspected pertussis cases should be reported to the Delaware Division of Public Health, Office of Infectious Disease Epidemiology at 302-744-4990 (Monday to Friday, 8:00 a.m. to 4:30 p.m.), 1-888-295-5156 (24/7), or by email at reportdisease@delaware.gov.

Recommendations 

Health care providers, daycare centers, early childcare education providers, schools, camps, and other places where children may congregate should work to ensure children, patients, and staff are current with pertussis vaccination. Pertussis vaccination guidelines can be found here: https://www.cdc.gov/pertussis/hcp/vaccine-recommendations/index.html.

Health care providers should recommend pregnant people get a dose of Tetanus, Diphtheria and acellular Pertussis (TDaP) vaccine during each pregnancy, preferably between 27 and 36 weeks gestation. Maternal antibodies provide protection to newborns before routine vaccination is recommended.

Adolescents should receive a dose of TDaP, preferably between ages 11 to 12 years. Adults who have not previously received TDaP should also be given a dose.

Treatment and Post-exposure Prophylaxis (PEP)

Early antibiotic treatment is recommended for all patients suspected of having pertussis to decrease symptoms and decrease the risk of transmission. If there is a high index of suspicion for pertussis or if the individual or their household members have risk factors for severe disease, treatment should be started prior to receiving test results. Advise patients with pertussis to remain at home until they have completed their treatment course. CDC provides guidance for treatment found here: https://www.cdc.gov/pertussis/hcp/clinical-care/index.html

Post-exposure prophylaxis (PEP) should be provided to all household contacts, close contacts, and contacts who have a high risk of developing severe pertussis within 21 days of their exposure to the case. High-risk populations typically include infants, women in third trimester of pregnancy, those with pre-existing health conditions, and those who have close contact with high-risk people such as health care workers. CDC provides guidance on PEP found here: https://www.cdc.gov/pertussis/php/postexposure-prophylaxis/index.html.

Additional Resources

CDC Pertussis

Clinical Overview of Pertussis

Clinical Features of Pertussis

Treatment of Pertussis

Laboratory Testing for Pertussis

References 

Centers for Disease Control and Prevention. (2026, June 11). About diphtheria, tetanus, and pertussis vaccination. Centers for Disease Control and Prevention. https://www.cdc.gov/vaccines/hcp/by-disease/dtap-tdap-td.html 

Centers for Disease Control and Prevention. (2026, June 11). Summary of pertussis vaccination recommendations. Centers for Disease Control and Prevention. https://www.cdc.gov/vaccines/?CDC_AAref_Val=https://www.cdc.gov/vaccines/vpd/pertussis/recssummary.html