Mpox Cases Are Dropping. Here's Why Investment in Testing Still Matters

Mpox (formerly known as monkeypox) cases in the United States have taken a nosedive since August and some regions may be close to stamping out the disease. New York City and San Francisco, once hotspots of the outbreak, have seen only a handful of new cases over the past few weeks.

Many of the people most vulnerable to infection are now vaccinated, thanks largely to the advocacy of the LGBTQ+ community and efforts of sexual health organizations. Still, experts warn that the outbreak isn’t over. And getting new cases down to zero now doesn’t mean the virus won’t rear its head again.

Throughout the outbreak, there’s been only one way to test for the virus: a swab of the telltale lesions and bumps associated with the disease. Lesions on the skin or inside sensitive areas, like the mouth and anus, are essentially little pockets full of viruses.

While the virus also circulates in blood and body fluids—like urine, sweat, and saliva—it can be harder to detect there. Because of this, the Food and Drug Administration said the lesion swab is now the only reliable way to test for mpox infection.

But some patients don’t develop lesions until days or weeks after being infected and developing other symptoms. By the time their results come back, patients may have suffered several days of uncomfortable symptoms or spread the virus to others.

“People were coming in requesting a test when they had no symptoms and they had no rash. The test for this infection is a swab of the rash and in fact, there is no other FDA-approved test. We need to have a rash in order to conduct those tests,” CDC Director Rochelle Walensky told a Senate committee in September.

Still, research from recent months indicates that tests based on throat swabs, saliva, and other bodily samples can also help identify cases.

Lesion tests must be performed in clinical settings, like doctors’ offices and sexual health clinics. Developing non-lesion testing that could be given at fairs or community events, in mobile testing vans, or even at home could help scientists keep tabs on the viral spread in this and future outbreaks.

“We’ve learned repeatedly that the earlier we can respond to an outbreak, the more effective we’re going to be controlling that outbreak,” said Jeffrey Klausner, MD, MPH, a clinical professor of population and public health science at the University of Southern California. “You can’t respond to something you don’t know about.”

A New Kind of Mpox Testing Is Underway

Testing for mpox before symptoms appear can be challenging. Patients don’t often come to their health provider seeking a test until after lesions appear, and early symptoms may be reminiscent of other sexually transmitted infections (STIs).

Benjamin Pinsky, MD, PhD, the medical director of the clinical virology laboratory at Stanford Health Care. His lab is often asked to test bodily fluid samples for STIs like gonorrhea and chlamydia.

When the lab runs these samples through an in-house mpox test, they can sometimes detect the mpox virus, even in samples from people without lesions. Pinsky said that there are more false negatives from non-lesion samples, compared to lesion swabs. Even so, screening for mpox cases while testing for other STIs could be helpful.

“Testing these specimen types, and particularly screening the high-risk populations, has some benefit to it,” Pinsky said. “That may be an important avenue for identifying individuals early on in the course of their illness and stopping chains of transmission.”

In a retrospective study from Belgium, 224 men submitted throat or anal swab samples for gonorrhea and chlamydia screening. When the researchers tested the samples for mpox, they found three asymptomatic cases.

Collecting anal or throat swabs might be the most effective ways to test for mpox in people without lesions. But saliva testing could also be effective, with the added benefit of being very easy and non-invasive to collect.

In a study published this month, researchers found 22 cases of mpox from 132 saliva samples. Among people with positive saliva tests, 18% didn’t have a rash at the time of testing. Among the patients who have positive lesion tests, 89% also had positive saliva tests.

Saliva tests might not be accurate enough to replace lesion swabbing as the main way to diagnose a patient. But they could pick up enough cases to identify presymptomatic and asymptomatic cases and keep tabs on where the virus circulates, according to Klausner, who is a lead author of the study.

The U.S. Is Flush With Tests, But Accessibility Is Still Lacking

For months, the U.S. has had more capacity to test for the disease than people seeking testing. As case rates climbed this summer, federal agencies ordered ever more tests, increasing the number of tests it could distribute in a week by more than 70,000. But the tests could be difficult to access.

Being able to test for mpox easily and in a widespread capacity will allow public health experts to keep tabs on cases and react more quickly if there are outbreaks in the future, Klausner said.

The problem, however, is that with fewer cases, there is less of a financial incentive to develop new tests. It’s often up to private companies to shoulder the cost of developing and evaluating new tests. During the COVID-19 pandemic, companies created at-home and saliva-based testing. But the incentive innovation was largely due to contracts and other financial support from the U.S. government.

“There are substantial costs. The federal government and Congress have to recognize the value of test development and make it easy for test developers to bring their products to market,” Klausner said.

In September, the FDA said laboratories could apply for emergency use authorization for mpox tests that are different from the official CDC kit. But the policies don’t include at-home testing or home specimen collection.

Introducing tests that can be done at home or in mobile clinics could improve access for people who live in states with laws restricting access to sexual health care.  

It’s also a matter of equity, Klausner said. In some regions of the U.S., and among Black men and other people of color, cases are actually increasing. Only 13% of the vaccine doses administered so far have gone to Black recipients, though they make up 35% of the cases.

“You can get an outside-the-clinic test on most street corners in the United States for COVID,” Klausner said. “It’s acceptable, it’s safe, it’s accurate. But for these STIs, including monkeypox, this doesn’t exist.”

Will Mpox Testing Become Part of an STI Panel Test?

This week, the CDC reported that in a study of 57 people hospitalized with mpox, 82% of them also had human immunodeficiency virus (HIV). More than 60% of people sick with mpox also had HIV or a different STI, according to a CDC study published in September.

“Our data tells us that monkeypox is not a disease that exists in isolation. It travels with HIV and other sexually transmitted infections,” Demetre Daskalakis, White House National Monkeypox Response Deputy Coordinator, said in a press call last month.

With the collision of mpox and other STIs, some experts say it could be useful to test for multiple infections at once. For instance, a throat or anal swab or a saliva sample from a patient seeking an STI test could be run for mpox as well. That would streamline the testing process and keep patients from needing to schedule separate appointments.

Some companies are working to develop such tests. Qiagen has a test for six different pathogens that present similarly: two forms of mpox, three herpes viruses, varicella-zoster virus, and enterovirus. This test is currently for research use only. In July, a California-based company called FlowHealth said it had developed a saliva-based test. The company has since removed information about the test from its site.

Whether non-lesion testing becomes a reliable way to diagnose mpox remains to be seen.

“I’d say we can hold off on putting it on every STI panel,” Pinsky said. “But at least for now, it seems like it’s worthwhile testing individuals, even if they don’t have lesions, if they’re engaging in very close contact in sort of high-risk situations.”

“Whether it becomes a part of a standard screening strategy will depend on whether this infection becomes endemic in the United States and in other countries where it has not been endemic before,” he added.