S2E47 What's in a Name: When Exposure Becomes Infection

How much virus does it take to cause an infection? In this episode, we're getting to the science behind the name Infectious Dose. We'll explore what happens between encountering a virus and becoming infected, why infection is a matter of probability rather than a fixed threshold, and how scientists measure something that's often impossible to observe directly in the real world. Along the way, we'll look at: What infectious dose and ID₅₀ actually mean Why exposure doesn't always result in infection How scientists measure infectious virus in the laboratory Why the route of exposure matters What norovirus, influenza, and measles teach us about transmission Whether a larger infectious dose means more severe illness How understanding infectious dose helps us prevent infections Full transcript and annotated scientific references in the companion blog post at InfectiousDose.com

In this episode of Outbreak Watch, we're tracking several outbreaks that are expanding, crossing geographic boundaries, or raising important questions about how well public health responses are keeping pace. New World screwworm continues to spread across the southwestern United States, with rising animal case counts and new detections that raise questions about surveillance, wildlife involvement, and the cost of responding to a threat once kept at bay through sustained prevention programs. In Washington state, H5N1 has now affected 40 dairy herds across two counties, with three human infections and one reported death. Meanwhile, the Bundibugyo Ebola outbreak in the Democratic Republic of the Congo has surpassed 10,500 confirmed cases, and secondary infections in Kenya and an imported case in Nigeria are complicating the regional picture. We also examine the latest measles developments in Pennsylvania and New York, including the death of a seven-month-old infant and why early MMR vaccination during outbreaks is different from the routine childhood schedule. Florida's locally acquired dengue cases continue into autumn, raising questions about whether cooler weather will interrupt transmission. And our international roundup covers yellow fever in Venezuela, cholera in Zambia, hand, foot and mouth disease in Vietnam, and Crimean-Congo hemorrhagic fever in Afghanistan. Throughout the episode, we focus on what's changed since our last update, what the evidence actually tells us, and what remains uncertain. See the companion blog post for sources and transcript.

We interrupt this program to bring you a brief bulletin... In the quiet town of Hawthorn Mill, a missing teenage girl has been found wandering barefoot along a country road. She remembers nothing. Authorities insist there's no reason for alarm. But the bulletins keep coming. For the final installment of Infectious Dose's Month of the Macabre, we're turning back the dial to 1938 with a special full-cast audio drama inspired by Orson Welles and the Mercury Theatre's legendary broadcast of The War of the Worlds. Through vintage radio programming, breaking news reports, and increasingly urgent transmissions, The Devil of Hawthorn Mill unfolds in real time as a small community confronts something it cannot explain. Put on your headphones, tune your radio, and stay with us. The broadcast is just beginning. A special Halloween production featuring our volunteer ensemble cast. This is a fictional audio drama. The events, community, and central illness are invented, although elements of the underlying science are real. Full episode transcript and cast acknowledgments available in the companion blog post on the Infectious Dose website.

One year. Three original hosts. Zero reliable scoring systems. It's the first anniversary of Outbreak After Dark, and the original campfire crew is back together! Heather welcomes Kate and Sam around the fire for a look back at the strange, hilarious, and occasionally horrifying moments that shaped Year One. Along the way, we explore how the show evolved from three friends talking about infectious disease into immersive storytelling, unexpected guests, and an increasingly elaborate collection of recipes with questionable names. And because we can't just have a normal anniversary celebration, Kate and Sam compete in an infectious-disease mini-game featuring forgotten quotes, survival decisions, and a mystery pathogen. The rules are clear. The judging is another matter. On the anniversary menu: The Menu of Misfortune—four recipes randomly selected from our first year, including House Call, Symbiosis Spritz, Rumor Mill, and Pecan Pustules. We're also looking ahead to Year Two, with new guests, Outbreak After Dark Gathering Kits, The Night Library, and the possibility of a full-fledged infectious-disease game show. Find the episode overview, downloadable transcript, and all four anniversary recipe cards in the companion blog post on the Infectious Dose website. Keep the embers warm. This is Outbreak After Dark.

An isolated village. A mysterious outbreak. A physician whose patients trust him with their lives. When American scientist Dr. Helen Seward travels to Romania's Carpathian Mountains to investigate cases of Crimean-Congo hemorrhagic fever, she expects to find infected ticks, complicated exposure histories, and a community struggling to contain a dangerous disease. What she finds is something far stranger. The ticks are appearing where they shouldn't. Medical records don't quite add up. And the village's beloved physician, Dr. Căpușan, seems to know more about the outbreak—and its unusual vectors—than he's willing to reveal. Inspired by Bram Stoker's Dracula, The House of Căpușan is an original Infectious Dose audio drama that brings infectious-disease science into the shadows of Gothic horror. 💀 Month of the Macabre 2026 🎬 This week's #SickFlicks: Bram Stoker's Dracula (1992) and Nosferatu (2024). Two atmospheric explorations of vampirism, contagion, and the dangerous intimacy of blood. 🎧 Headphones recommended. This is an immersive, audio-only story. 🩸 Next week: It's the final week of Month of the Macabre, and we're celebrating with two special releases! Original Outbreak After Dark cohosts Kate and Sam return for an anniversary reunion with the original trio back together. Then, on Friday, October 30—the 88th anniversary of the 1938 War of the Worlds radio broadcast—we're bringing you The Devil of Hawthorn Mill, an original audio drama inspired by Orson Welles' legendary broadcast. 📻 Tune in to WIDX. The broadcast is about to be interrupted. Visit the episode blog post for the overview and downloadable transcript.

Just a Little Wider | Month of the Macabre He's already been waiting more than an hour. He's sick, exhausted, and ready to leave. But the dentist can see him now. Surely it won't take long. Then the dentist finds something unusual. As the exam continues, the patient grows increasingly ill. The dentist's behavior becomes more disturbing. Familiar sounds begin to suggest terrible things, and with every passing minute, it becomes harder to tell whether the danger is coming from the person holding the instruments, or from something happening inside the patient's own body. Inspired by the real possibility that systemic infections can leave clues in the mouth, Just a Little Wider is an immersive work of medical horror in which illness, perception, and reality become impossible to separate. 💀 Month of the Macabre 2026 — An original Infectious Dose horror story. 🎬 This week's #SickFlicks: Dead Ringers (1988) and The Autopsy of Jane Doe (2016)—two unsettling films about medical authority, the vulnerability of the human body, and exams that take a horrifying turn. 🎧 Headphones recommended. Find the complete episode transcript and more at Infectious Dose.

In this week's Outbreak Watch, we're examining the latest developments in the DRC Ebola outbreak, Pennsylvania's ongoing measles outbreak and a new development in the US H5N1 outbreak. Finally, we separate evidence from speculation surrounding reports of a possible laboratory-associated infection in Russia. Outbreak Watch is part of Infectious Dose, bringing you outbreak developments, epidemiological context, and the science behind the headlines. Find the full transcript, annotated sources, and additional resources at Infectious Dose.

The museum is closed. The exhibits aren't finished changing. In the first episode of Month of the Macabre 2026, a routine after-hours visit to a museum of infectious disease history takes an unexpected turn. Past the familiar scenes of Broad Street, the 1918 influenza pandemic, and SARS in Toronto, a new gallery has appeared: a modern train station displaying an outbreak that hasn't happened yet. Then the exhibit changes. And changes again The Collection is an immersive Infectious Dose audio story about infectious disease history, transmission, outbreak investigation, and what happens when knowing the future doesn't necessarily mean you can control it. 🎬 This week's #SickFlicks to accompany the episode: Annihilation (2018) and The Endless (2017)—two stories in which reality begins behaving according to unfamiliar rules, leaving the people inside to figure out what those rules mean. Check out the companion blog post for citations and transcript.  🎧 Headphones recommended.

It’s horror movie night, but Heather can’t stop seeing infectious disease in the monsters. Heather is joined by her friend Valerie to explore the real biology behind some of horror’s most enduring fears: tuberculosis and vampire lore, rabies and werewolves, zombies as outbreak epidemiology, neurological disease and possession, and the strange biology behind The Last of Us, The Thing, and Alien. Plus, Valerie plays the hilarious Horror Movie or Medical Literature? and discovers that when it comes to horror, evolution has had a considerable head start. So grab a drink, pick a movie, and remember the most important public-health lesson horror has apparently failed to teach us: stop hiding bites. Annotated citations and episode recipes available in the companion blog post. 

How do eight people get falciparum malaria in Germany when none of them traveled somewhere malaria is circulating? The answer may be that they didn't have to travel. The mosquito did. This episode follows the investigation into a cluster of malaria cases linked geographically or occupationally to Frankfurt Airport, including three deaths. We'll look at how an infected mosquito can carry malaria across continents, why airport malaria can be difficult to diagnose, what previous cases tell us about this rare phenomenon, and what investigators still don't know about the current outbreak. Find annotated citations and transcript in the companion blog post on the Infectious Dose website.