What Is Invasive Group A Streptococcal Disease (iGAS) and How to Diagnose Strep A Infection?
With the unexpected increase in invasive group A streptococcal disease (iGAS) infections, experts around the world are increasingly urging attention to risks posed by Strep A. While strep A typically causes benign, mild, and self-limiting diseases that can be easily cured with antibiotic treatments, such as strep throat, invasive group A streptococcal disease (iGAS) infections can lead to severe diseases such as necrotizing fasciitis and streptococcal toxic shock syndrome. With growing efforts to raise awareness for the signs and symptoms of strep A infections, health authorities are looking into the upsurge in the notifications of invasive group A streptococcal disease (iGAS) after several deaths among children and other at-risk groups. Read along to learn more about strep A and invasive group A streptococcal disease (iGAS), their symptoms, and their diagnosis.
What is strep A?
Strep A or streptococcus A is a group of bacteria that typically infect the throat and skin. Predominantly comprised of bacteria of the species S. Pyogenes, Streptococcus A (Strep A) causes various non-invasive and invasive diseases of mild to life-threatening severity. A significant portion of strep A infections is asymptomatic. Therefore, people often contract and transmit these infections unwittingly through direct contact with mucus or sores on the skin. In addition to diseases such as strep throat, impetigo, and scarlet fever which are directly caused by infection with streptococcus A (Strep A), these bacteria also lead to certain inflammatory diseases that develop as a result of the immune response of the body after infection such as post-streptococcal glomerulonephritis and rheumatic fever. Indeed, the Strep A Vaccine Global Consortium (SAVAC) reports that of the estimated 500,000 deaths caused by Streptococcus A (Strep A) infections each year, rheumatic heart disease accounts for approximately 350,000. In contrast, the remaining deaths are attributed to acute infection.
What are the symptoms of infection with streptococcus A (Strep A)?
Streptococcus A (Strep A) causes various diseases with different clinical presentations and severity. Accordingly, the signs and symptoms of infection vary depending on the location of the infection and the particular disease it causes. For example, Strep throat, one of the most common infections caused by streptococcus A (Strep A), is a mild and self-limiting disease presenting with symptoms such as throat ache, difficulty swallowing, white nodules in the throat, throat redness, and swollen tonsils. Scarlet fever, on the other hand, predominantly affects children and causes a rarely severe disease with symptoms such as fever, sore throat, body aches, and skin rash. If the bacteria infect the skin, streptococcus A (Strep A) can cause impetigo, which is an infection characterized by symptoms such as red skin sores that leave a yellow crust, blisters, itchy rash, and swollen lymph nodes.
What is invasive group A streptococcal disease (iGAS)?
Invasive Group A Streptococcal Disease (iGAS) is a severe infection that occurs when Streptococcus A (Strep A) gets beyond the immune defenses of the infected person to infiltrate parts of the body that are typically free from these bacteria, such as the blood, muscles, or lungs. Invasive group A streptococcal disease (iGAS) may develop as a result of the inability of the host immune system to fight off the bacteria or due to the presence of skin sores and breaks that facilitate the entry of the bacteria. Accordingly, groups at higher risk of developing invasive group A streptococcal disease (iGAS) include individuals with low or compromised immunities, people with chronic illnesses that affect the immune system, such as cancer or HIV, drug users, and those on specific treatments or therapies.
Often presenting with initial signs such as high fever, severe myalgia, localized muscle tenderness, or redness at the site of a wound, invasive group A streptococcal disease (iGAS) may manifest as many different clinical syndromes such as pneumonia, abscesses, meningitis, bacteremia, necrotizing fasciitis, and streptococcal toxic shock syndrome (STSS). Necrotizing fasciitis is a life-threatening skin infection caused by “flesh-eating bacteria.” In contrast, streptococcal toxic shock syndrome (STSS) is a severe complication where multiple organ systems malfunction due to infection. Altogether, invasive group A streptococcal disease (iGAS) has a case-fatality rate of around 30%. It is estimated that invasive Group A streptococcal disease (iGAS) causes over 500,000 deaths each year, which, together with rheumatic heart disease (RHD), places streptococcus A (Strep A) among the top ten causes of infectious disease mortality in the world.
How are strep A infections diagnosed?
Diagnosing streptococcus A (Strep A) infections often involves throat culture or antigen detection. The throat culture is a laboratory diagnostic method that detects the presence and growth of bacteria in throat swab samples. Methods based on antigen, on the other hand, determine the infection status of the patient by targeting proteins specific to streptococcus A (Strep A). Due to its speed and convenience, rapid antigen testing is widely accepted as the primary method for diagnosing streptococcus A (Strep A). Since it takes much more time and resources, a throat culture is often recommended for use with at-risk groups to confirm the infection status and detect infections that rapid strep tests may have missed.
Often coming in the form of lateral flow assays, rapid antigen tests for strep A typically require collecting an oropharyngeal swab sample. After the sample is collected and processed as instructed, the test kit delivers qualitative results in no more than 15 to 20 minutes. Designed to assist the diagnosis of streptococcus A (Strep A) in patients with clinical and epidemiological risk factors, rapid antigen tests such as our Strep A Rapid Test Kit offers a quick, accurate, and highly convenient method that allows the patients to safely start a course of antibiotics against the detected infection as soon as they receive a positive result.
Cole, J. N. S., Barnett, T. C., Nizet, V., & Walker, M. (2011). Molecular insight into invasive group A streptococcal disease. Nature Reviews Microbiology, 9(10), 724–736. https://doi.org/10.1038/nrmicro2648
Piper, S. F. (2014). Group A Streptococcal Peptides expressed in HBsAg-S VLPs as a vaccine candidate. University of Southern Queensland.