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Thursday, September 8, 2011

The Cough That Won't Quit


The View from the Office


The Cough That Won't Quit:
Pertussis in Portola

     In the middle of this past Winter I wrote an article about the cold that wouldn't quit--that keeps hanging on with a deep cough for 6 to 8 weeks. There I reported that most of that was due to bronchospasm triggered by the infection, which was best treated with an albuterol inhaler or comparable medication.
     There was one other cause of cough that won't quit which I didn't mention then because it is much more rare. But now that we have seen several cases of pertussis (whooping cough) in Portola, it is worth discussing this and explaining how it differs from common post-viral bronchospasm.


                                        The Pertussis Quandary

     In Plumas County we're now seeing several confirmed pertussis cases. Pertussis (whooping cough) has always been a confusing, poorly understood, commonly misdiagnosed, and always seriously underestimated clinical infection. It is not entirely clear that we know a whole lot more now (in 2011) about this organism than I did when I started my career. Nonetheless, here is a recent update.(1)

    
     The first pertussis vaccine was developed in the 1930s and became routine in the 1940s. A majority of us have probably had the vaccine. A few of us can remember having the classic whooping cough when we were young. One problem is that childhood vaccination  confers only limited immunity that wanes after 5 to 10 years and rarely lasts more than 12 years. Another problem is that having the pertussis infection does not leave you with good antibodies against pertussis. Thus one never knows how protected the population is, but whatever it is, it's waning fast.  Another problem is that the immunization prior to the 1990s had a lot of significant side effects; in particular, there was concern (overblown as it turns out) that pertussis vaccine could cause brain damage. This led many parents to elect to forego vaccination for their children. We are now seeing the results of this reduced immune protection in the general population.
    Classic pertussis presents in 3 stages: a 2 week catarrhal (mucousy) stage with nonspecific symptoms like an ordinary cold in which it is nearly impossible to make the diagnosis; the astute clinician might notice unexplained excessive lacrimation (tearing) and/or conjunctival redness. 
     The paroxysmal stage begins in the 2nd weeks and lasts for 2 to 3 months. The onset of paroxysmal cough is the hallmarkA paroxysmal cough is defined as a series of coughs occurring during a single expiration; these tend to occur in groups throughout the day and night with few or no symptoms in between. "A cough paroxysm causes low lung volumes, leading to a vigorous inspiration that may result in a whoop, particularly in infants and children, in whom the caliber of the trachea is smaller." Listen to these classic whoops. [Click on link.] 
     The final phase is the convalescent phase in which the cough slowly disappears over 2-3 months. 
     So the total illness can run for 6-7 months.

     Unfortunately for modern clinicians whose patients have been previously immunized (or  infected), the characteristics of the cough illness are atypical and may manifest just as chronic cough. Several recent epidemiological studies have shown that pertussis is present as the cause in 12-32% of prolonged cough illness in adolescents and adults.
    Once you suspect pertussis, which test do you use? Alas, there is no good choice. The CDC endorses only the culture and PCR (a specialized DNA assay) methods for diagnosis in community practice. Culture, however, lacks sensitivity (will miss a lot of cases), and PCR lacks specificity (it will be positive in a significant number of people who do not have pertussis infection). Swabs for testing need to be obtained on Dacron swabs since cotton is toxic to B Pertussis and calcium alginate swabs interfere with PCR assay. "Importantly, the  sensitivities of PCR, serologic testing, and, particularly, culture decrease with the duration of illness." Direct fluorescent antibody testing (DFA) is inexpensive and rapid but is no longer recommended because of its poor sensitivity and specificity. Serologic testing (with serial titers showing 4-fold change) is useful for epidemiological research, "but is neither widely available nor standardized and no FDA-approved test exists." Thus, in practice, there are many more people who have pertussis as a cause of their chronic cough than we are able to identify on testing.
The CDC Case Definition: The CDC clinical case definition for endemic or sporadic cases of pertussis is a cough illness lasting 2 weeks or longer without other apparent cause with 1 or more of the following:
  • paroxysms of coughing (sometimes leading to a faint, called tussive syncope)
  • inspiratory whoop (more likely in children) [Click on link to hear what it sounds like.]
  • post-cough vomiting
Alas, again--"Importantly, our data do not apply to an outbreak setting [like now in California] in which the pretest probability of pertussis for a patient with a cough illness may be substantially higher and the thresholds to test and empirically treat for pertussis may be lower...[A]n important finding in this study is that the absence of classic symptoms of pertussis may not have sufficiently low probability to exclude the diagnosis of pertussis, and the presence of classic symptoms is common in patients who do not have evidence of pertussis infection."
COMMENTSo what is a reasonable clinician to do?
    In the epidemic context, just treat everyone with cough > 3 weeks to prevent secondary spread.
    In the sporadic case context, test with PCR (if available) or culture after 3 weeks, and treat empirically after 8 weeks.
    I was interested to note that, just before our current epidemic in California had started, I had seen an abrupt increase in patients seeking evaluation for cough > 8 weeks duration (i.e., 4 patients in a 2 month period). None of them were ultimately diagnosed with pertussis, most likely due to the quality of the available tests; but in retrospect I sure do believe that they had pertussis. Of course, it doesn't help them or anyone very much to diagnose it in retrospect.

                            The Bottom Line for Patients

1. If you have persistent cough for more than 3 weeksconsider being treated for pertussis. If you have cough for 8 weeksdefinitely get treated for pertussis. This won't cure you, but it will protect everyone you come into contact with.

2. The treatment is with azithromycin (250 mg tablets); 2 tablets for the first dose, then 1 a day for 4 days. Persons who live with a patient with this infection should also be treated.

3. Understand that treatment prevents the spread of pertussis from one person to another, and is therefore highly advisable from a community health perspective. Treatment does NOT alter the course or symptoms of pertussis infection. Thus patients may have symptoms for up to 2 to 3 months even after treatment. Try not to blame your doctor.

4. The current recommendation is that all adults receive at least one pertussis vaccine booster (called a TDaP). You should receive the vaccine even if you have actually had pertussis infection because the infection does not lead to good antibody levels. 
     Best yet, ask your doctor for this immunization way before you ever get sick.



Reference: 
Cornia PB et al. Does this coughing adolescent or adult patient have pertussis? JAMA 2010; 304(8): 890-6.

4 comments:

  1. I've had this persistent cough, as described on this site for about two months, maybe longer at a less extreme level, and after three visits to my doctor, the last one this afternoon, he's considered 'whooping cough' -I'd never considered it myself; never entered my thinking. It's a very distressing cough. I will not be surprised if it isn't whooping cough from all what I've read in the last 30 minutes.

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