Health officials in Annapolis are issuing an urgent advisory this week as a highly contagious respiratory illness begins to surge across the state, complicating an already busy winter viral season.
While Maryland hospitals have been managing flu and RSV cases since December, doctors are now flagging a sharp increase in Pertussis (Whooping Cough)—often called the “100-Day Cough” due to its lingering and exhausting symptoms.
Surveillance data indicates that the outbreak, which began in Pennsylvania and Delaware, has moved down the I-95 corridor. Maryland is now seeing significant community spread, particularly in the densely populated suburbs surrounding Baltimore and Washington, D.C.
The Hotspots: Where is it Spreading?
The infection is currently tracking highest in counties with dense school districts and commuter hubs. Health officials have identified the following “high transmission” zones:
- Harford County: Specifically in the Bel Air and Aberdeen areas, where cases have spilled over from the Pennsylvania border.
- Baltimore County: Urgent care centers in Towson, Essex, and Owings Mills are reporting a spike in patients with severe, non-stop coughing.
- Montgomery County: School officials in Bethesda and Silver Spring have sent notices to parents regarding confirmed cases in classrooms.
- Prince George’s County: A smaller but growing cluster has been identified near College Park.
Emergency departments at Johns Hopkins and MedStar Health are urging residents to avoid the ER for mild coughs but to seek immediate help if they experience difficulty breathing.
Is it a Cold, the Flu, or the ‘100-Day Cough’?
Pertussis is dangerous because it is a “master of disguise.” For the first week, it looks exactly like a common cold, leading many Marylanders to inadvertently spread it to family members.
Here is how to distinguish the “100-Day Cough” from other viruses circulating in Maryland right now:
| Symptom | The ‘100-Day Cough’ (Pertussis) | 2026 Flu Strain |
| Cough Type | Violent, uncontrollable fits; may end with a “whoop” sound or vomiting. | Dry, steady cough. |
| Duration | Long (Lasts 2 to 12 weeks). | Short (Lasts 5 to 7 days). |
| Fever | Usually mild (low-grade) or no fever at all. | High fever (100°F+) that hits suddenly. |
| Key Sign | You often feel fine between coughing fits. | You feel exhausted and achy all the time. |
Warning for Parents: Infants are the most vulnerable. They may not “whoop” at all. Instead, watch for them turning red or blue during a cough, or if they seem to stop breathing (apnea). This requires immediate emergency care.
Why is This Happening Now?
Maryland health experts point to a “gap in immunity” as the primary cause.
- Waning Protection: The Tdap vaccine (which protects against Pertussis) loses effectiveness after about 10 years. Most adults in Maryland have not had a booster since they were teenagers.
- The “Post-Holiday” Effect: The surge in travel along the East Coast during the holidays likely accelerated the spread into Maryland communities.
The Action Plan: What to Do Today
- Check Your Vaccine History: If it has been more than 10 years since your last Tdap shot, you are likely unprotected. Pharmacies like CVS, Walgreens, and Giant Food across the state have confirmed supplies of the booster.
- The “Vomit” Test: If you or your child is coughing so hard that it causes gagging or vomiting, do not send them to school or work. Ask your doctor for a PCR test for Pertussis specifically.
- Cocoon the Vulnerable: If you have a baby at home or an immunocompromised relative, ensure that anyone who visits them has been boosted recently. This “cocooning” strategy is vital to preventing hospitalization in infants.
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