Part of me feels like I should be saying, “Sorry!!!” for bringing up this issue. No one really wants to hear about it. On the other hand, a bigger part of me thinks, “Why should I be sorry for telling people about an actual health threat that is backed up by current medical research and isn’t widely discussed? After all, it could potentially save a life.”
So I’m going to ruin your day.
Here we go…
You and your kid are at risk for pertussis.
Even if you are vaccinated…
…Even if your child is vaccinated…
…Even if that ice cream party at your kid’s class worked and everyone in your kid’s class is vaccinated…
…And even if you don’t have any symptoms…
You’re all at risk for pertussis. Or more accurately pertussis and parapertussis.
(Quick note on whooping cough and bordetella pertussis- whooping cough is the illness caused by the bacteria Bordetella pertussis. Our current vaccines are only for the bordetella pertussis strain of the bacteria, but other strains are out there like Bordetella holmesii and now Bordetella parapertussis. More parapertussis in a minute.)
If we could describe the current state of affairs for pertussis control with a Facebook relationship status, it would be: “It’s complicated”.
The CDC started noticing a rise in pertussis cases in pertussis cases back in the 1980’s. There have been a four different hypotheses for this: 1) waning immunity from vaccination or natural infection 2) evolution of the B. pertussis bacteria to escape protective immunity 3) low vaccine coverage and more recently 4) asymptomatic transmission from individuals vaccinated with the currently used acellular B. pertussis vaccines- in other words, you’re vaccinated, not showing any symptoms and still spreading the disease.
Pertussis and Waning Immunity
Waning immunity doesn’t explain the rise because waning immunity would occur mostly in older age groups as their immunity dies off. But the rise was seen across all age groups.
The Switch from DTP to DTaP
The acellular pertussis vaccine (DTaP) that is currently used is supposed to be less effective than the older whole cell pertussis vaccine (DTP) that was used until the 1990’s. But there’s a catch to the old DTP vaccine- it had a higher rate of both mild and serious adverse events. (How serious was “serious”? Long story short, multiple large case-control studies found that babies who received the DTP vaccine were more likely to develop encephalopathy- a term that is used for brain damage, disease or malfunction. And follow-up showed that ten years later that children who had experienced a serious neurologic illness after receiving DTP were more likely than children in the control group to have chronic nervous system dysfunction ten years later. If you want the long story, you can read it here- the stuff on DTP starts on page 22. This is an interesting read from a public health perspective. It’s the September 6, 1996 Weekly Morbidity and Mortality Report from the CDC. It’s interesting to kind of take a ride in a time machine and understand what the CDC was looking at around the time the DTP vaccine was removed from the American schedule.
But it still couldn’t account for many cases. For example, in 2005 there was an outbreak in Lithuania where DTP was still in use and 75.7% of the children who had laboratory confirmed pertussis were fully vaccinated with DTP.
Low Vaccine Coverage
This has received the most media attention, but is probably the least likely to account for the rise in pertussis. If you look at the CDC’s chart of reported pertussis cases between 1922 and 2015, rates of pertussis have been rising despite the widespread use of Tdap vaccines for adults. There are some places where vaccine coverage is lower, but low vaccine coverage can’t account for the resurgence of pertussis in these areas because pertussis cases have been found in vaccinated individuals and in infants who were “cocooned”. For example, Boulder, Colorado is known for having lower rates of vaccination, which made it a great case study for low vaccine coverage. An article in the Atlantic from 2002 tried to examine the pertussis resurgence from this perspective. But in the middle of his piece though, the author is confronted with a paradox and states: “Although unvaccinated children are six times as likely as vaccinated children to get whooping cough during an outbreak, about half the cases in Colorado have involved vaccinated children.” Even with low vaccine coverage, vaccinated children were not getting anywhere near the levels of expected protection.
An outbreak of pertussis in San Diego presented a similar problem. Of the 1,000 adults and children who tested positive for pertussis in 2010, over half had been vaccinated. A survey of nine other counties in California showed that between 44 and 83 percent of individuals with pertussis had been immunized.
Another example is a case from Israel in 2000 where a vaccinated 4 month old baby died of pertussis despite the parents, siblings, aunt and all the children at the siblings’ day care centers being vaccinated with DTP. The report examined 46 fully vaccinated children, five of whom tested positive for pertussis with laboratory diagnostic testing (not just basis of symptoms), Only two of those children met the World Health Organization’s diagnostic criteria for pertussis. The study concluded that even vaccinated, asymptomatic children can be carriers of pertussis.
And so we come to…
Asymptomatic transmission of pertussis
Asymptomatic means that you aren’t displaying any symptoms. Discussion of asymptomatic transmission of pertussis has mostly been in medical and epidemiology journals- though the CDC has hinted at this in their information for the public:
“If you get pertussis after getting pertussis vaccines, you are less likely to have a serious infection. Typically, your cough won’t last as many days and coughing fits, whooping, and vomiting after coughing fits won’t occur as often. When vaccinated children get pertussis, fewer have apnea (life-threatening pauses in breathing), cyanosis (blue/purplish skin coloration due to lack of oxygen), and vomiting.”
Althouse and Scaprino (2015) found that asymptomatic transmission was the best fit for the observed changes in pertussis. It explained the changes in age-specific attack rates, the increased genetic diversity within the bacteria population, the increasing incidence and the failure of the “cocooning” strategy to protect infants. They also noted that asymptomatic transmission might bias assessments of vaccine efficacy that are made only on observations and not on laboratory confirmed testing.
Adults and teens may not display the “whoop”, they may have a very long, lingering cough. Of course, the tricky part is that a long, lingering cough can be caused by many things. Estimates are that 10-30% of long, lingering coughs are pertussis– but many of these cases may not be reported, which also makes the number of pertussis cases seem deceptively low.
Bordetella Pertussis has Adapted
In 1998, Dutch researchers used to DNA sequencing and found that the protein composition of Bordetella pertussis has changed. Bordetella pertussis proteins (P.69) are an important component in vaccines. Pertussis vaccines use the P.69A type of Bordetella pertussis proteins. That worked well for a while. Within the Dutch population, P.69A was the dominant type of pertussis in circulation from about 1949 to 1980. But in 1981, two different types emerged P.69B and P.69C. Within the Dutch population, these became the predominant Bordetella pertussis proteins circulating. Though Bordetella pertussis P.69A,B, and C are 93% similar, the vaccine only protects against P.69A. Basically, the bacteria adapted to a new threat- similar to what we’ve seen with antibiotic resistant strains of bacteria.
A study from Italy had similar findings: “Molecular analysis suggests that also in Italy B. pertussis strains differ from those included in the current vaccine.”
Bacteria are not smart, but considering that they can produce a new generation in hours, they are very adaptable.
CDC has also hinted at this too:
“CDC is evaluating potential causes of increasing rates of pertussis, including changes in disease-causing bacteria types (“strains”). Unlike a foodborne illness where one strain causes an outbreak, multiple types or strains of pertussis bacteria can be found causing disease at any given time, including during outbreaks. Research is underway to determine if any of the recent genetic changes to pertussis bacteria may contribute to the increase in disease in the United States.”
Bordetella parapertussis is a species of the Bordetella bacteria that causes whooping cough as well. Pertussis vaccines do not protect against it because it is a different species of Bordetella pertussis. But the resulting illness is very similar. There is no vaccine for it. Certain antibiotics can be used for it- at least for now. Estimateas are that parapertussis accounts for anywhere between 1% and 35% of Bordetella outbreaks. California’s public health department has put together an information sheet on it here.
Now obviously, if it’s 1% that’s not an enormous threat, but if 35% of Bordetella infections are parapertussis, it could actually be extremely common. There are other strains of Bordetella too like Bordetella bronchiseptica and Bordetella holmseii
So What CAN We Do?!
Right now, we treat pertussis with antibiotics- but this isn’t exactly a “cure”. It’s not the actual infection with the bacteria that kills a person- it’s the secondary complications like pneumonia. Antibiotics can kill the bacteria bordetella pertussis, making the patient non-infectious, but antibiotics can’t actually halt the progression of the disease. Secondary conditions like uncontrollable vomiting, hypoxia, and dehydration can result from the severity of the coughing. This is why pertussis remains difficult to treat even with antibiotics. And (more bad news) antibiotic resistant strains of pertussis have recently been isolated .
EVERYONE needs to be aware of the risk of pertussis transmission and parapertussis transmission. You should always assume that you could spread a bordetella infection and please do not assume that herd immunity will protect your baby.
- Since cocooning hasn’t been effective at protecting infants, the CDC recommends that pregnant women get a Tdap shot in their third trimester with the idea that the mother will pass the antibodies through the placenta to her baby before birth. However, this will not protect against parapertussis or P.69B and C type pertussis.
- Transmission mostly occurs through contact with saliva and mucus of an infected person. Wash your hands frequently and if you have a baby make sure everyone who is contact washes their hands frequently and keeps coughs and sneezes contained (vampire cough).
- Breastfeed as much as you can. Antibodies against pertussis can be passed through breastmilk and can help give a baby further protection. Breastfeeding alone can’t protect against pertussis, but it may offer some degree protection. Though it hasn’t been studied, hypothetically speaking breastfeeding could give your baby some degree of protection against parapertussis and P.69 B,C pertussis since the mother’s body will adapt to produce antibodies to antigens in the environment. The relationship between pertussis and breastfeeding still isn’t fully understood, but it’s a good idea!
- Limit your baby’s contact with large crowds- especially in the first six months. Reduced exposure=reduced risk.
- If you think your baby may have pertussis or parapertussis, get him into the hospital right away. The further the secondary complications progress, the greater the chances of death. Earlier treatment=better chances of survival.
How Worried Should I Be???
Pertussis rates are still much, much, much lower than they were during the 1920’s and 1930’s. (Though asymptomatic cases and cases in teens and adults mean that these numbers are not a complete representation of pertussis transmission.) Parapertussis is still not a notifiable disease, so it’s hard to know exactly how many cases are out there. Definitely take adequate precautions and be aware of all forms of pertussis and parapertussis, but chronic diseases still pose the greatest threats. The CDC gets about 10,000 to 40,000 reported cases per year and about 20 deaths per year are attributed to pertussis- most in young babies. By comparison, there were about 1,685,210 new cases of cancer diagnosed in the United States in 2016 with 595,690 deaths. In 2014, 1,960 children died of cancer. Or another comparison, in 2011-2012 5,300 children and young adults under the age of 20 were diagnosed with type 2 diabetes. If you have a baby and want to understand how breastfeeding might impact pertussis (and several other diseases), please see my “Breastfeeding and Immunity” class for more info on how to protect your baby.
So this post may have been a little on the depressing side. So let’s lighten things up a bit:
Life is still good.