Definition and Comment
Pertussis is a highly contagious bacterial disease that affects the respiratory system and produces spasms of coughing that typically, in small children, end in a high-pitched inspiratory whoop; thus the name whooping cough.
Pertussis rates are on the rise across the country. This may be due in part to increased physician awareness and testing but may also be related to decreased immunization rates. The falling rates of appropriate childhood immunizations are of public health concern.

Causes, incidence, and risk factors
Pertussis is caused by infection with the Bordetella pertussis bacteria. The infection is spread through the air by respiratory droplets from an infected person. The incubation period is between 5 and 21 days with an average range of 7 to 10 days.
Whooping cough can affect people of any age. Prior to the advent of widespread immunization, the disease was evident predominantly in infants and young children. Now that the majority of children are immunized in infanthood, a higher percentage of cases are being seen among adolescents and adults.

Though early immunization (see childhood immunization schedule) has decreased rates of pertussis in the very young, about 38% of recognized cases still occur in infants younger than 6 months of age. Young infants are at particular risk of long-term effects or death due to pertussis.

The Disease
Once inhaled, the Bordetella pertussis bacteria quickly take up residence in the upper airway and proceed to infect the trachea and lungs. Initial symptoms (catarrhal stage) resemble a common cold: mild upper respiratory complaints, low-grade fever, and mild cough. One to two weeks after onset, however, episodes of spasmodic coughing ensue (paroxysmal stage). These may be accompanied by post-tussive vomiting or choking, inspiratory whoop, facial cyanosis and even syncope. In infants under the age of six months, apnea is not uncommon and may be more prevalent than an actual whoop. School-aged children seldom whoop.

Complete recovery may take weeks or even months. Coughing episodes lessen during this convalescent stage, but may be exacerbated by other respiratory infections. It may take months for the cough to resolve completely.
Though vaccinated individuals can contract pertussis, symptoms are generally less severe and may be difficult to differentiate from other respiratory infections. For this reason, pertussis often goes undiagnosed. Incompletely vaccinated young children and infants are in danger of severe illness when they are exposed to unknowingly infected siblings, parents, or playmates.

Testing and Diagnosis:

Note: The CDC recommends a culture and PCR as the "gold standard" for diagnosis of pertussis.
• PCR testing: The NY State lab and certain other reference facilities perform this testing. It is quite sensitive and is considered a confirmatory test for pertussis by the CDC. Check with your lab about the availability of this testing method.
• Culture of secretions from the nose and mouth: Bordetella pertussis is very “picky” about growth media and is not easily isolated on culture. A positive culture is considered confirmatory, but a negative culture alone, does not rule out infection.
• DFA testing: Not as sensitive as the PCR. Although recommended in the past, it has fallen into disfavor and is not currently regarded as a confirmatory test for pertussis by the CDC.
• CBC: White blood cell count may be elevated and characterized by large numbers of lymphocytes (lymphocytosis).
• Serologic (blood) tests: Though still used by some clinicians, antibody testing for pertussis is not considered useful or diagnostic by the CDC. Serologic studies are not recommended for first-line testing.
o IgA (Quantitative). Establishes evidence of early/acute infection in the following way: Patients with acute infection develop IgG, IgM, and IgA antibodies.
o Following vaccination, IgG and IgM antibodies can be demonstrated, except in infants where IgA antibodies do not develop.
If you are suspicious that your patient has or might have pertussis, obtain appropriate media from your lab and perform a naso-pharyngeal swab. Test kits for pertussis vary between labs. It is important to know which tests your lab performs.
1. PCR: may take a week to result.
2. Pertussis culture: may take 3-10 days and if negative, does not rule out disease.
3. DFA: may take 1 – 2 days to result and is not recommended.
As always, treat your patient according to your own clinical judgment.

Treatment
Erythromycin (or Zithromax) may shorten the duration of the symptoms if initiated early enough. Unfortunately, most patients are diagnosed well after the period of time when antibiotics are most effective. Antibiotics do decrease the communicability of pertussis, however. Patients are communicable for 21 days after cough onset. This is decreased to 5 days, when antibiotics are initiated. Household members and close contacts should receive prophylaxis (Zithromax or Erythromycin).

Infants under 18 months of age require constant supervision because breathing may temporarily stop during coughing spells. Infants with severe cases should be hospitalized. An oxygen tent with high humidity may be used. Intravenous fluid may be indicated if coughing spells are severe enough to prevent adequate oral fluid intake. Sedatives may be prescribed for young children.

Cough mixtures or expectorants and cough suppressants are usually not helpful and should not be used.

Prognosis
In older children, the prognosis is generally very good. Infants, however, are at risk for severe disease. The pertussis mortality rate in infants less than 6 months of age is 0.5% to 1%.

Complications
• Slowed or stopped breathing (apnea)
• Pneumonia
• Convulsions due to lack of oxygen
• Nose bleeds
• Ear infections
• Brain damage from lack of oxygen (anoxic encephalopathy)
• Bleeding in the brain (cerebral hemorrhage)
• Seizure disorder (permanent)
• Developmental retardation
Prevention

Pertussis is a reportable disease in New York State. All suspected and confirmed cases of pertussis should be reported to the local health department by physicians and laboratories. Public Health officials are responsible for insuring that all cases of pertussis are reported to the CDC and that all potential contacts are identified and prophylaxed. Of particular concern are small infants and children.

Vaccination in infancy helps protect young children but is not 100% effective. In addition, immunity wanes over the years. Previously vaccinated individuals may develop atypical or very mild disease that goes unrecognized and may unknowingly expose young children. Fortunately, two types of pertussis booster vaccines have recently become available: Boostrix for 10 – 18 year olds and Adacel for 11 – 64 year olds. Individuals over the age of ten years, who require a tetanus booster, should receive a one-time dose of Tdap. Health care professionals, especially those who work routinely with infants, should receive a booster dose of Tdap, as well. Additional recommendations, contraindications and precautions are available in the December 1, 2006 issue of the MMWR, General Recommendations on Immunization at http://www.cdc.gov/mmwr/preview/mmwrhtml/rr5515a1.htm?s_cid=rr5515a1_e.

Children under the age of nineteen who do not have access to vaccination for any reason should be referred to their local health department where vaccination can be obtained for a nominal fee or at no charge.

4/12/2007