Microbiology: A Systems Approach 4th Edition by Marjorie Kelly Cowan

Exercise 47

Whooping Cough in Washington
In 2012, Washington State experienced an epidemic of pertussis, more commonly known as whooping cough. Pertussis is a bacterial disease caused by Bordetella pertussis, an aerobic gram-negative coccobacillus that is highly transmissible via respiratory droplets. Whooping cough is a name derived from a characteristic symptom exhibited by many affected by the disease: a paroxysmal (violent) cough followed by a sharp intake of breath that sounds like a "whoop." In the first 6 months of 2012, there were 2,520 cases of pertussis in Washington State, compared to 180 cases in the same period of the previous year. Incidence of the disease was highest among children less than a year old and children between the ages of 10 and 14, and among the Hispanic population as well. The statewide incidence of pertussis was 37.5 cases per 100,000 compared to the rate of 4.2 cases per 100,000 nationwide.
Reported cases of pertussis were confirmed by clinical and state health laboratories through culturing of patient specimens. The samples were also subjected to polymerase chain reaction (PCR) analysis for molecular typing of the microbe. This nucleic test led to a rapid diagnosis of disease in patients because the tests detect the presence of microorganisms in a sample without culturing.
What are the limitations of culture methods and PCR analysis in the diagnosis of pertussis
What other diagnostic methods were used in diagnosing pertussis in this outbreak
Although bacterial culture of nose and throat swabs is the standard protocol for diagnosing pertussis, B. pertussis is often difficult to culture under laboratory conditions since it is a fastidious organism. Obtaining quality specimens from patients is also a challenge, especially if they have already received antibiotic. Culture methods are also time-consuming and can delay treatment if pertussis is suspected. PCR is sometimes used because a positive diagnosis can be made rapidly. However, sometimes false-positive or false-negative results can occur, and PCR is only optimally sensitive during the first 3 weeks of the pertussis cough.

Pulse-field gel electrophoresis (PFGE), a type of DNA fingerprinting, was performed by the Centers for Disease Control and Prevention (CDC) in the Washington State outbreak. The DNA profiles generated from the samples taken from patients were compared to a national database of PFGE profiles of B. pertussis. According to the CDC, 54% of the isolates represented the 4 most common isolates of B. pertussis, 20 isolates represented the 7 less common isolates, and five samples had PFGE profiles that had not been seen in the CDC database previously.
Pertussis is part of the standard DTaP (diphtheria, tetanus, and pertussis) vaccination series. What was the reason for such a large increase in cases of pertussis from 2011 to 2012