Over the last six months I have tested seven patients for both pertussis and group A strep antibodies. What is my score?

Four positive pertussis IgG tests.
Two positive streptozyme tests*.
One negative for both.

And this means?

It's quite complicated.

Pertussis is whooping cough. We are having our third outbreak in five years in my county. Whooping cough can kill babies under six months, because they tend not to whoop. They have apnea instead. That means they stop breathing. This is bad.

Do the four positive pertussis IgG tests mean the people had whooping cough?

The answer is maybe, maybe not.


The gold standard current test for pertussis is a nasal swab for the virus. The first patient that I wanted to test had a huge deductible. The nasal swab was going to cost over $300. So the lab called me in a sort of panic need an answer right now mode. I said check if the blood draw IgG is cheaper. It was. So we did the blood draw. It was positive.

Pertussis is a notifiable condition, that is, I am supposed to report it to the Health Department so that they can check contacts and track the epidemic. So I reported it. But the state does not count the IgG because it is a human antibody test, not a test of the actual virus. And the pertussis IgG can be elevated not only with pertussis but also with other walking pneumonias:mycoplasma pneumonia, chlamydia pneumonia and legionella as well as pertussis.

So why did I do the blood test in 6 more people instead of the nasal swab?

The nasal swab is only accurate for the first 3-4 weeks. After that the virus is not in the nasal cavity so the test will be negative. All 6 more people came in having had a cough for more than a month, usually two months. I was trying to distinguish walking pneumonia from my experience with strep A. The treatment for walking pneumonia is currently zithromax (azithromycin) or levaquin. Levaquin has that nasty rare side effect of breaking the achilles tendon so mostly I choose zithromax. Only I didn't with that first patient because they were allergic to macrolides, including zithromax. Again I guessed first and looked it up afterwards: clindamycin. Yep, good guess.

With the first patient I called the health department and said "I did the wrong test and used the wrong antibiotic." Once we went over the why, she agreed that I'd made the best second choices for both.

When the streptozyme came back positive, I used penicillin. With one patient the case was as weird as mine so we used both oral penicillin and oral clindamycin. I talked to both pulmonology and infectious disease specialists. Pulmonology basically said, "Ok." Infectious disease thought it was maybe overkill to use both.... but didn't object.

So does the streptozyme mean they had strep? Again, maybe yes, maybe no. I am testing for a streptoccus A antibody, so what the human produces. Could it be something else? Yes, but it looks like streptococcous to the body. And it seemed resistant to azithromycin in me and responded to penicillin. That could be true resistance or it could just be that the zithromycin was not nearly high enough a dose. For legionella you double the usual zithromax dose. Are you confused yet? Is this more complicated than "positive strep test"? Well, yes. Medicine is more complicated than a it appears: that is, the strep test works except when it doesn't. Since there are currently 6000 identified strains of streptococcus A, I don't know if I am trying to track a weird strain from my little solo clinic or if I have something else by the tail feathers.....

So anyhow, the ones with positive pertussis IgGs got better with azithromycin and the ones with the positive streptozyme got better with penicillin. So far so good.

Zika virus reminds us that the viruses and atypical bacteria and bacteria don't stay the same. They reproduce faster than us. They trade genes with each other. They go from chickens to ducks to people. And yet if we kill our gut bacteria we kill ourselves. A deep respect for mother nature seems indicted: if we mess with her, she will win.

Get your influenza shot, and update your tetnus to the Tdap (tetnus, diptheria, acellular pertussis), since the old tetnus shot was the Td (tetnus, diptheria). Yearly on the flu, every ten years for the Td......So far the US is having a quiet influenza year but it can spike fast and it takes two weeks for the vaccine to work.

*I did a strep throat test first, which was negative. Before doing a blood test.

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