How to tell a viral infection from a bacterial infection

Recently, the United States Food and Drug Administration granted approval to a technology for distinguishing between viral and bacterial infections within minutes. The technology, MeMed BV, works through MeMed key platform, decoding the host immune response to the infection to differentiate between viral and bacterial infection.[1]

The MeMed Key platform, which enables rapid and sensitive measurements of multiple proteins at the point-of-the need, has been approved for both children and adults.[1] The test is an automated, semiquantitative, immunoassay (chemiluminescence-based analyte measurements of patient serum samples) that measures three host proteins – TNF-related apoptosis-inducing ligand (TRAIL), interferon γ-induced protein 10 kDa (IP-10), and C-reactive protein (CRP) - in adult and pediatric serum samples. The test is indicated for use in conjunction with clinical assessments and other laboratory findings, in patients with suspected acute bacterial or viral infection, who have had symptoms for less than 7 days.[2]

Many a times, the initial symptoms produced by both viruses and bacteria are similar, namely fever, sore throat, and cough, thus making them clinically indistinguishable. This may result in inadvertent use of antibiotics for viral infections, for which they are ineffective. This misuse of antibiotics may lead to emergence of resistance to antibiotics. Thus, timely and proper diagnosis is the key for effective management and this test promotes timely diagnosis when the infection site is inaccessible or when the pathogen is undetectable using conventional tests. This test will be handy even when the cause of infection is new emerging pathogen. As such, this test will enable timely and better informed antibiotic treatment decision, thus promoting rational use of antibiotics.

The MeMed BV test result is a score between 0 and 100 derived from computational integration of the measurements of the three proteins, namely TRAIL, IP-10, and CRP, where low scores are indicative of viral infection and high score of bacterial infection – 0 ≤ score ≤10: high likelihood of viral infection (or other non-bacterial etiology); 10 < score <35: moderate likelihood of viral infection (or other non-bacterial etiology); 35 ≤ score ≤65: equivocal; 65 < score <90: moderate likelihood of bacterial infection (or co-infection); 90 ≤ score ≤100: high likelihood of bacterial infection (or co-infection). The test run time is approximately 15 mins.[2]

The Food and Drug Administration clearance was based upon a prospective, multicentric, observational, blinded study, carried out by enrolling both pediatric and adult patients.[3] The test provides highly accurate results with area under the curve of 90% and 97% for primary and secondary endpoints, respectively. The test will prove highly useful for distinguishing viral from bacterial infections in pediatric population, particularly in emergency setting.

References

As you may know, bacterial infections can be treated with antibiotics. However, antibiotics are often overused and authorities now caution against using them for things like viral infections, which aren't affected by antibiotics. So, how can you tell the difference?

You can't. At least, you can't without help from a healthcare provider.

You may be tempted to try diagnosing your own infection at home without seeing the doc, either because you want to save money or time. You might figure if it's a viral infection and you can't get any help from antibiotics, what's the reason for going to the healthcare provider?

There is no reason for everyone with a common cold needs to go running to the healthcare provider, but there are a couple of problems with making your decision based whether or not you think it's a viral infection or not.

1. Depending on the type of viral infection, there may still be medications that can help. The medicines specifically targeting viruses are called antivirals. They're not used as often as antibiotics, but in some cases they help a lot.
2. There's absolutely no way to tell if an infection is caused by bacteria without a test. There are some telltale signs that help point us in the right direction, but unless it's life-threatening, most docs will take a sample before doling out antibiotics. The sample taken depends on the suspected infection, and can include a blood sample, throat culture, skin swab, or more.

The desire to diagnose at home is human nature, but rather than wondering if the infection is viral or bacterial, instead focus on whether you need to see a healthcare provider.

Here are some good rules of thumb when trying to decide whether to see the doc. Make an appointment if you see any of the following:

• Dehydration. Mom always wants to bring you chicken soup when you're sick. The healthcare provider always tells you to drink clear fluids (chicken broth counts). Staying hydrated helps you thin out the mucus your body is producing. While your immune system fights infection -- of either type -- it uses mucus to carry away the virus or bacteria from the body. If the mucus is too thick, say from dehydration, the infection could get worse. Indeed, bacteria can take hold in mucus that was originally produced while your body was fighting a virus.
• Shortness of breath. If an infection is attacking your lungs or airways, it's time to see the doc. Pneumonia or asthma with bronchitis can become life-threatening if not treated promptly and appropriately.
• Weakness, confusion or fainting. Combined with the usual suspects of fever, chills and body aches, any version of fatigue or weakness is a sign of serious infection.
• Suddenly getting worse. If you're plugging along, especially if it feels like you might be beating this thing, and suddenly you feel worse, it's probably time to see the healthcare provider. Sometimes one infection opens the door to another. Like I said already, mucus produced by viral infections can sometimes be a great place for bacteria to grow.
• Kids with fevers. Fevers are a common part of viral illnesses in children -- most of which improve with supportive care (fluid, medicine to bring down the fever, and perhaps a big dose of TLC). Talk to your healthcare provider about situations that might require a visit to the healthcare provider.

You may have heard that green mucus or a wet cough is a sign of a bacterial infection. It might be true that green snot is a sign that something is growing in there, but it doesn't exclude the possibility that something else caused the infection in the first place. Either way, base your decision of whether to go to the healthcare provider or not on how you feel.

Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.

1. Kramer LD. Overview of Viruses. Merck Manual Professional Version.

2. American Lung Association. Pneumonia Symptoms and Diagnosis.

Additional Reading

• Andre M, Gröndal H, Strandberg E-L, Brorsson A, Hedin K.Uncertainty in clinical practice – an interview study with Swedish GPs on patients with sore throat.BMC Family Practice. 2016;17:56.doi:10.1186/s12875-016-0452-9.
• Shapiro, D., Lindgren, C., Neuman, M., & Fine, A. (2017).Viral Features and Testing for Streptococcal Pharyngitis.Pediatrics,139(5), e20163403. doi:10.1542/peds.2016-3403
• Steed AL, Stappenbeck T.Role of Viruses and Bacteria-Virus Interactions In Autoimmunity.Current opinion in immunology. 2014;0:102-107.doi:10.1016/j.coi.2014.10.006.

By Rod Brouhard, EMT-P
Rod Brouhard is an emergency medical technician paramedic (EMT-P), journalist, educator, and advocate for emergency medical service providers and patients.

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