Pertussis

Pertussis, also known as Whooping cough is a contagious bacterial respiratory infection known for causing severe coughing.

Prevelence
From 1940 to 1945 an average of 175,000 people (about 1 in in 670 population) got pertussis each year in the US (about 1 in in 670 people). The first pertussis vaccine was introduced in the 1940s and greatly reduced the incidence of pertussis. From 2008 to 2017, an average of 24,385 people (about 1 in 13,000) got pertussis each year in the US.

Transmission
Pertussis is spread by respiratory secretions including airborne droplets.

Symptoms and complications
Symptoms start 4 to 21 days (often 7-10 days) after exposure, although in rare cases symptoms may not start until 42 days post-exposure. Illness begins with the gradual onset of cold-like symptoms, with a cough that gradually worsens for 1-2 weeks, by which time it is quite severe, with bursts (paroxysms) of numerous, rapid coughs, apparently caused by difficulty expelling thick mucus. Paroxysms are often followed by a whooping sound as the person inhales suddenly, as well as vomiting and exhaustion.

Paroxysms occur regularly for 1-6 weeks (sometimes up to 10 weeks), after this, the cough gradually subsided over a 2-3 week period, although paroxysms can reoccur with subsequent respiratory illness months later. The force of coughing is in some cases enough to break ribs or cause serious internal injuries.

From 1998 to 2017, about 1 out of 2,000 reported pertussis cases resulted in death1|[calc] although many of these people were vaccinated, and vaccination tends to reduce the severity of the disease.

Pertussis is most serious in infants, the following rates of complications are reported in children less than 1 year old, according the CDC.

Prevention
In the US, DTaP vaccines are given to young children to immunize them against diphtheria, tetanus, and pertussis, these DTaP vaccines are about 84-85% effective at preventing typical pertussis, and 71-78% effective at preventing mild pertussis. In addition a Tdap vaccine is given to older children and adolescents, Tdap is similar to DTaP, but contains a lower dose of diphtheria and pertussis vaccine. 73% of people vaccinated with Tdap are completely immune to pertussis 1 year later, and 34% are still completely immune 4 years later.