It's been an eventful week for me but relatively quiet in the world of infectious diseases. I've just returned from a week's trek in the semi-wilds of Colorado. You may recall that last week's post included a mention of mosquitoes and high altitudes, noting that climate warming has been accompanied by trends of more mosquitoes at those upper elevation. I'm happy to report that after spending the week in the great outdoors at 5000 - 10,000 feet I only had a few bites and didn't even touch my insect repellent.
Turning skyward, I was able to view the September 17 partial lunar eclipse from Mesa Verde National Park; sadly my antique cell phone camera was unable to capture it. This morning I consulted my trusted 2024 print edition of The Old Farmer's Almanac to remind myself of the difference between an equinox and a solstice. The earth's axis is tilted at 23.5 degrees from the perpendicular as it revolves around the sun, and the equinoxes occur when both northern and southern hemispheres equally face the sun. Northern hemisphere solstices occur when the North Pole is most tilted towards (winter) or away (summer) from the sun. I learned so much this week!
Pertussis
Whooping cough was in the news recently, though really this is just a return to "normal" after the pandemic years. Here's the long view from CDC data.
On a more recent view, you can see the age breakdown.
I was involved in pertussis immunology and vaccine research very briefly in my career. I always like to mention an oldie-but-goodie article from 1992 showing that about one-quarter of UCLA college students with cough lasting longer than 5 days showed evidence of recent pertussis infection. It's a good reminder that pertussis in adults usually looks very different, and milder, than the classical whooping cough in infants. Diagnosis is difficult unless you think about pertussis as a possbility.
Maybe not so coincidentally with these news reports, the FDA VRBPAC meeting last Friday focused on using Controlled Human Infection Models (CHIMs) to try to develop a better pertussis vaccine. Yes, that's right, intentional infection of human volunteers to study various aspects of the disease. We need more information to improve pertussis control, given that our current acellular vaccines are less effective (but also with less side effects) than the predecessor whole cell vaccines. Large scale trials are difficult, expensive, and largely impractical in the present era, so it's time for new approaches. A group at the University of Southhampton in the UK presented some preliminary data from a CHIMs trial and also had a nice graph to put into perspective relative mortalities and contagiousness of pertussis compared to other pathogens:
The study itself was just a challenge study of human volunteers to determine the dose of organisms and the immunologic responses surrounding infection and colonization. It seems likely that these types of studies will be utilized more frequently in the future to improve our understanding of pertussis prevention.
Needless to say, I didn't join this meeting live, I was off the grid in Colorado, but I did skim through the recording and slides today. This wasn't a typical VRBPAC meeting where voting occurred, it was more of a discussion to guide future research.
More Wastewater
Speaking of returning to pre-pandemic levels of infection, I've been watching wastewater trends for enterovirus D68. You may recall that this was an enterovirus strain that figured prominently, but not exclusively, in outbreaks of acute flaccid myelitis that tended to occur in even-numbered years - pretty strange.
As you can see, the pandemic really ended this pattern, and nothing new is going on so far this year. However, wastewater numbers, at least for EV D68, have looked very different.
Will we see a blip upwards in AFM cases this year? I hope not.
More Colorado Learning
My landscape designer wife clued me in to the details of the quaking aspens, so named due to the fluttering of the leaves that have their own distinct sound. They are beautiful, both my wife and I wished we had better pictures to show you.
On another note, although I love to learn, one new factoid I happened upon was perhaps less exciting. Hiking at these altitudes, I learned that I'm not as young as I used to be!
Not your topic this week - but are the R0 and the case fatality rate in this graph correct ???
For other readers, note that Dr. Schwartz clarified that he was asking specifically about the covid numbers in the graph. Of course the main point of the slide was the very high reproductive number for pertussis, in the range of measles and extremely high compared to any other bacterial infection.
First a note about reproductive numbers. It's very common to see variation in results from different studies of the same pathogen. First, these calculations are at best estimates and often are associated with a large confidence interval. Second, the calculation relies on knowing the number of susceptible people in the population. That's not terribly difficult for measles if one knows the vaccination rates in that population and vaccine effectiveness, both of which are pretty straightforward; measles immunity from vaccine or natural infection is lifelong, until immunity wanes either due to immmunocompromising condition or in the very elderly. For SARS-CoV-2 however, it's very difficult to know the number of susceptible people because a) it can change with new variants; b) protection against infection from either vaccine or natural infection is relatively low, plus a lot of infections are asymptomatic; and c) immunity wanes with time after vaccine or infection. I don't think anyone knows a precise reproductive number for covid nowadays.
The graph shows an extremely high case fatality rate for SARS-CoV-2. I went back and listened to the presentation and to the question and answer period following it, and there was nothing mentioned about the covid point on that graph. That didn't surprise me, everyone at the meeting was focused on pertussis. So, I started to hunt around for mortality estimates. I couldn't find anything as high as 20% anytime during the pandemic, but I did find something close. One recent publication looked at mortality rates globally over time and shows about 10% mortality early in the pandemic; note that the graphs in this article have a log scale on the y axis. So, case fatality rates early in the pandemic were around 10% in many areas of the world, including the US.
I then visited my old reliable Johns Hopkins University covid site. They quit recording data in March 2023, but their mortality estimates at that time, including the entire pandemic time, showed rates in the US at 1.1%; Peru had the highest at 4%.
So, I don't know where the 20% mortality rate came from, but it's not far off from what was seen early in the pandemic.
I hope this clarification helps, and thanks for asking a question that probably a lot of other readers wondered about.