Whooping cough is contagious from the start of cold-like symptoms until at least 2 to 3 weeks after the coughing begins; 5 days of the right antibiotics ends contagiousness much sooner.
The trap is timing: the first week or two masquerades as a cold, and that is when spread is most efficient. Antibiotics given early protect the people around you (they end transmission at 5 days) even though they barely shorten the cough once the fits start. Household exposure triggers its own rulebook: close contacts, especially infants, third-trimester pregnant women, and the immunocompromised, often get preventive antibiotics, because infant pertussis is the dangerous form. Stay home from work or school until 5 full days of antibiotics are complete, or 3 weeks from cough onset untreated. Vaccination (DTaP for kids, Tdap for adults and every pregnancy) is the prevention backbone, though vaccinated people can still catch and transmit milder cases. The cough outlasts the contagiousness by weeks to months; the "100-day cough" nickname is earned, and a lingering cough alone does not mean you are still infectious.
What to do
Common questions
How long is whooping cough contagious?
Whooping cough (pertussis) is contagious from the moment cold-like symptoms start, which is maddening, because the first week or two looks like an ordinary cold and that is exactly when spread is most efficient. The CDC's window: people can spread the bacteria from the start of symptoms until at least 2 weeks after the coughing fits begin, and without treatment the contagious period can run about 3 weeks from cough onset. Antibiotics change the math completely: 5 days of an appropriate antibiotic (a macrolide like azithromycin) ends contagiousness, which is why early treatment matters for everyone around the patient even though it does little to shorten the cough itself once the fits start. The exposed-household rules: close contacts, especially infants, pregnant women in the third trimester, and anyone immunocompromised, are often given preventive antibiotics (postexposure prophylaxis) even if vaccinated, because infant pertussis is the lethal version of this disease. Work and school: stay home until 5 full days of antibiotics are done, or 3 weeks from cough onset if untreated. Vaccination status matters for prevention (Tdap for adults, DTaP for kids, and a Tdap dose in every pregnancy), but vaccinated people can still catch and spread it, just usually milder. The cough itself outlasts contagiousness by far: the "100-day cough" nickname is earned, with fits lingering for weeks to months after you are no longer infectious.