How Mpox Is Diagnosed

Medically reviewed by Michael Menna, DO

Like many other viruses, mpox (formerly known as monkeypox) cannot be diagnosed by symptoms alone. Although infections are sometimes treated based on symptoms (typically in areas where an outbreak is occurring), lab testing is needed to confirm the diagnosis and ensure that mpox is the cause and not some other disease.

Mpox is diagnosed with lab tests that detect genetic evidence of the virus from a swab of a skin sore. Blood tests and other lab tests may be used to rule out diseases that look similar to mpox, such as chicken pox or syphilis.

This article walks you through what is involved in diagnosing mpox, including when mpox testing is recommended.

Self-Checks

While you may assume you have mpox because you've been in contact with someone who has it, the signs and symptoms can vary from one person to the next. In the early stages, there may only be mild, flu-like symptoms (like fever, headache, muscle pain, and fatigue) or no symptoms at all.

The first recognizable sign of mpox is the appearance of a characteristic blister-like rash on the skin. Although rash symptoms can vary, there are some tell-tale signs to look out for, including:

• Rash distribution: Typically, the rash starts on the face before moving to the trunk and then elsewhere on the body, such as on the palms of the hands and soles of the feet.

• Sexual exposure: If the virus is transmitted through sexual contact, the rash may start on the groin, genitals, or anus and either remain there or spread to other parts of the body, such as the arms, trunk, legs, and face.

• Number of rashes: The rash may involve only one or two pimple-like bumps or as many as 200 or more bumps.

• Rash appearance: The bumps rapidly grow into firm, blistery lesions filled with clear fluid and then pus. These pus-filled bumps eventually burst and scab over.

• Pain and itch: The bumps can be extremely painful until they burst, after which the sores are more itchy than painful as they start to heal.

Who Is at Risk?

During the 2022 outbreak in the United States, most mpox cases were among men who have sex with men (MSM) exposed through intimate or sexual contact. Even so, the Centers for Disease Control and Prevention (CDC) reports that anyone can get mpox regardless of age, race, ethnicity, sex, gender identity, or sexual orientation.

Related: How Do You Get Mpox?

Physical Exam

Most people seek a diagnosis for mpox after a painful, unexplained rash develops. The diagnosis typically starts with a review of your symptoms, medical history, and risk factors for infection (including recent sexual exposures).

The healthcare provider will then perform a physical exam to check for the usual signs and symptoms of infection.

With mpox, the rash will develop in a characteristic pattern—from bumps to blisters to pus-lesion lesions—before breaking open and crusting over. They tend to develop and evolve simultaneously. Those occurring around the anus may be accompanied by rectal pain, bleeding, or a pus-like discharge.

The timing of the rash outbreak is also key as it tends to develop three to 17 days after a suspected exposure.

How Mpox Differs

One of the signs that differentiates mpox from similar viral infections like chicken pox is lymphadenopathy (swollen lymph nodes). With mpox, swollen lymph nodes may appear behind the ear, below the jaw, in the neck, or in the groin, often before the rash even appears.

Related: Symptom of Mpox You May Not Know

Labs and Tests

Mpox is diagnosed definitively with a swab of an open sore. The swab is then sent to a lab for evaluation using polymerase chain reaction (PCR) technology.

PCR works by amplifying (multiplying) the genetic material of the virus, called DNA, to levels at which it can be positively identified. PCR testing is used to diagnose many diseases and to customize treatments based on the characteristics of the person's DNA.

Only a healthcare provider can order an mpox test. The provider will usually either take the swab themselves or send you to a lab to get one. They may also order a collection kit to be sent to your home for you to perform the sample collection.

Here is what to expect when undergoing mpox testing:

• The healthcare provider will rub the swab vigorously over open lesions to obtain a sample of fluid and cells. More than one lesion will be swabbed.

• The procedure may be a little uncomfortable, but obtaining an ample quantity of genetic material is necessary.

• Once the swab is submitted to the lab, the test results should be returned within a few days.

• Until the results are received, you will be advised to take standard precautions to avoid spreading the virus to others.

CDC Testing Recommendations

According to the CDC, testing is only recommended for people with a rash consistent with mpox. Because the test relies on a sample of fluid from a lesion, it is of little value if you have no lesions.

What Test Results Mean

The results of the mpox test, called the orthopoxvirus PCR, are pretty straightforward and mean one of the following:

• Positive: This means that you have mpox and need to take precautions to avoid transmitting it to others until you are completely recovered. You are considered contagious until all scabs have fallen off and the skin beneath has amply healed.

• Negative: This means that no evidence of mpox DNA was found and you probably do not have mpox. Even so, you should continue to take steps to protect yourself and others.

• Inconclusive: This means that the results of the test are unclear (usually because not enough of a specimen was obtained) and the test needs to be repeated.

Related: Mpox in the US: Cases by State

Differential Diagnosis

Although mpox has distinguishing features (such as pain and swollen lymph nodes) and tends to occur in outbreaks (including the 2022 outbreak affecting over 100 countries), the signs and symptoms are often distinguishable from many other viral and non-viral diseases.

Because of this, your healthcare provider may opt to run other blood, tissue, or urine tests to rule out conditions with similar features. This is referred to as a differential diagnosis.

Among some of the conditions that may be explored in the differential diagnosis are:

• Bacterial skin infections: This includes impetigo, which causes oozing, blister-like sores, and methicillin-resistant Staphylococcus aureus (MRSA), which causes painful, oozing bumps.

• Chicken pox: This is a highly contagious infection caused by the varicella-zoster virus (VZV) that triggers an outbreak of itchy, fluid-filled blisters (usually starting on the trunk).

• Drug allergy: Also known as drug hypersensitivity, these reactions can sometimes cause a widespread outbreak of blistering rash, including serious ones like Stevens-Johnson syndrome (SJS).

• Eczema herpeticum: This is a serious condition associated with herpes simplex virus type 1 (HSV-1) that causes fluid-filled blisters on the face and neck that spread to other parts of the body.

• Genital herpes: This is a sexually transmitted infection (STI) mainly linked to herpes simplex virus type 2 (HSV-2) that causes an eruption of painful, blistering sores on the genitals, groin, or anus.

• Scabies: This is a parasitic infestation that causes an outbreak of intensely itchy, pimple-like bumps on the underarms, elbows, wrists, fingers, navel, breasts, buttocks, or genitals.

• Syphilis: This is a bacterial STI caused by Treponema pallidum that usually manifests with a single, painless ulcer on the genitals or anus.

Summary

While mpox may be recognized by the outbreak of a painful, blister-like rash, it can only be diagnosed with a lab test. The test involves a swab of fluid from an open sore, which is sent to a lab for evaluation. The results are usually received within a few days.

Other lab tests may rule out infections or diseases with similar features, such as genital herpes, MRSA, or chicken pox.

A Word From Verywell

If you think you've been exposed to mpox, don't wait until symptoms appear; tell your healthcare provider as soon as possible. Mpox vaccines are available which may help avert the infection if given within four days of the exposure.

Vaccination is also advised for men who have sex with men (MSM) if they have had group sex, sex in a commercial sex venue, or multiple sex partners within the prior two weeks. The same applies to transgender or gender-diverse people who have sex with men.

Read Next: Where to Get Vaccinated for Mpox

Frequently Asked Questions

How long does mpox last?

Most people recover from mpox within two to four weeks. Symptoms usually start within three weeks of exposure to the virus. The initial flu-like symptoms may be followed by a rash one to four days later.

How do you treat mpox if you get it?

There are no specific treatments for mpox. But, because the viruses that cause mpox and smallpox are similar, an antiviral drug used to treat smallpox, called tecovirimat (TPOXX), may help. TPOXX is generally reserved for those who are at risk of severe infection, such as people with advanced (human immunodeficiency virus (HIV).

Can mpox kill you?

Mpox, a viral infection similar to smallpox, is rarely fatal. Of the roughly 60,000 infections reported worldwide in 2022, only around 20 deaths have occurred. With that said, mpox can be excruciatingly painful for some people and can cause permanent scarring.

Read the original article on Verywell Health.