April 24, 2014

Whooping cough

Here in the Pacific Northwest of the United States, we are in the midst of a pertussis epidemic. Which begs the question – once there’s an outbreak, what should we do? There’s the public health answers like respiratory etiquette, don’t cough on people, keep infected kids out of school, vaccinate. But what should we do in the emergency department when we have a patient with confirmed or even suspected pertussis? Should we give them antibiotics, should we give their household members antibiotics? Do antibiotics even work against pertussis? These are some of the questions asked in  a 2009 Cochrane review titled Antibiotics for Whooping Cough.

Whooping cough is caused by the Bordetella bacteria and epidemics specifically by Bordetella pertussis. The acellular pertussis vaccine series is about 80% effective but begins to wane after 5 to 10 years. Thus the need for a booster. Eighty percent efficacy isn’t perfect, but it’s better than 0%, which is what you get with no vaccine. So why not just let pertussis float around the community and cause an epidemic here and there? For most adults, it’s going to be a nasty cough that goes on for a while and it’s the same case for older kids. But for the very young, infants, it’s not such a benign disease. They can develop severe respiratory infection, encephalitis and even die. Pertussis is also extremely contagious. Between 70 and 100% of household and up to 80% of school contacts become infected.

Pertussis is bad cough, really bad for babies, extremely contagious and happens in epidemics. We can partially prevent it with vaccination but not completely. So the next question is, can we treat it?

Treatment:

Do antibiotics achieve eradication of Bordetella pertussis? In other words, do they get rid of the bug? Yes, they do. If you give the right antibiotic, which we’ll get to in a second, your patient will be effectively treated for infection. Which brings up the next question…

Do antibiotics improve the clinical illness of whooping cough? You would think that if the bug is gone, the symptoms would improve. But the answer to this question, based on the available evidence is: no, symptoms do not improve.  So as you write the antibiotic prescription, you might be thinking, “Good on you my patient, you’re going to get less people sick and you’ll give a nice handshake to public health, but that cough you’ve got, nothing I can really do about it.”

Take the information on lack of  clinical improvement with a grain of salt however, because there’s not a lot of quality data out there comparing placebo and treatment groups with pertussis infection. When I say not a lot, I mean very very little. But when your patient comes back in a week after taking antibiotics and they still have the cough, this is a potential piece of education to say that more antibiotics aren’t necessarily the answer. With the data to date, according to the Cochrane reviewers – antibiotics can make your patient non infectious but they will still feel like they are.

What antibiotics to use and for how long? Macrolides are the mainstays of pertussis treatment. Erythromycin, clarithromycin, azithromycin all work well. TMP/Sulfa is a good backup when your patient returns with abdominal pain and vomiting after a few days of macrolide. Look to the end of this post for dosing schedules.

Should you treat suspect cases? Your patient has an intense cough or maybe a cough that’s not going away after a few weeks and you think, “Hmm, could be pertussis.”  There is no clear right or wrong answer here. You don’t want to overtreat and you don’t want to undertreat. Is that patient going to die if you delay treatment a day or two until their studies come back? Likely no. Are you going to shorten their course of illness? Likely no. Are you going to limit duration of infection and window of transmission? Possibly yes. In my practice, if I really suspect pertussis, I test and start treatment.

What to do in household or close contact exposure? Should those living with, or in prolonged close proximity to, a patient with pertussis receive prophylactic antibiotics? The Cochrane review found that for close contacts, there is insufficient evidence to show that prophylactic antibiotics give benefit for either development of symptoms or development of positive Bordetella pertussis culture. For the general population, prophylactic antibiotics are not recommended – with one exception:  infants less than 6 months old, although that cutoff is often stretched to one year of age. This is the group with the highest risk of severe morbidity or even mortality from pertussis.  Give chemoprophylaxis to infants, pregnant women in their third trimester (since they will soon be in contact with an infant),  and anyone who could potentially expose an infant (childcare workers, those with infants at home, etc.). This is not a hard science based recommendation, but infants are a high risk group at greatest risk of morbidity/mortality and  have not yet had a full series of pertussis vaccinations.  Prophylaxis for infants is recommended by the Cochrane reviewers as well as the Centers for Disease Control.

CDC recommendations for treating pertussis:

Azithromycin

  • Infants aged <6 months: 10 mg/kg per day for 5 days.
  • Infants and children aged >6 months: 10 mg/kg (maximum: 500 mg) on day 1, followed by 5 mg/kg per day (maximum: 250 mg) on days 2–5.
  • ** Cochrane review has 3 days of azithromycin at 10mg/kg/day as an acceptable choice
  • Adults: 500 mg on day 1, followed by 250 mg per day on days 2–5.

Clarithromycin

  • Infants aged <1 month: not recommended.
  • Infants and children aged >1 month: 15 mg/kg per day (maximum: 1 g per day) in 2 divided doses each day for 7 days.
  • Adults: 1 g per day in two divided doses for 7 days.

Erythromycin

Editor’s note: Since the time course of treatment is longer and side effects often greater with erythromycin, count on lower compliance

  • Infants aged <1 month: not preferred because of risk for IHPS (pyloric stenosis). Azithromycin is the recommended antimicrobial agent. If azithromycin is unavailable and erythromycin is used, the dose is 40–50 mg/kg per day in 4 divided doses. These infants should be monitored for IHPS.
  • Infants aged >1 month and older children: 40–50 mg/kg per day (maximum: 2 g per day) in 4 divided doses for 14 days.
  • Adults: 2 g per day in 4 divided doses for 14 days

TMP/Sulfa

  • Infants aged <2 months: contraindicated.
  • Infants aged >2 months and children: trimethoprim 8 mg/kg per day, sulfamethoxazole 40 mg/kg per day in 2 divided doses for 14 days.
  • Adults: trimethoprim 320 mg per day, sulfamethoxazole 1,600 mg per day in 2 divided doses for 14 days.
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Comments

  1. Mike Jasumback says:

    Rob,

    I am still alive, just wayyyyy behind. The toughest question that has hit me wrt pertussis, is; If you treat, why test? And what about the incompletely immunized or the elderly, shoudl we treat and immunize???
    MIke

    • Mike, with the incomplete resistance and waning protection from a successful vaccination, the right answer is not black or white. Is it ever?
      Testing isn’t going to make a difference for the infected patient (except for peace of mind of a defined dx), they are already on the path to a month of hacking cough. But from a public health standpoint, testing gives some useful information both for near contacts and the community as a whole. I i
      As far as your other question, that is a chin scratcher.

  2. Do adults really need to take TMP/Sulfa for 14 days??? Seems quite a long duration??

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