Rapid Diagnostic Test for Respiratory Infections

With the onset of winter, there is an increase in acute respiratory infections caused by various respiratory pathogens recently. As a consequence of acute respiratory infections, every year, coinciding with the seasonal epidemics of influenza and RSV, there are excessive demands on the healthcare system, resulting in an increased number of visits and the overloading of the A&E Department, increased consumption of antibiotics and an increase in the performance of analytical and imaging tests. As in other infectious processes, swift accurate diagnosis is associated with more targeted and effective treatment, lower transmission of the disease and, often, a reduction in its duration. 

Immunochromatographic tests are currently among the most frequently used rapid diagnostic tests owing to their ease of use and rapid results (10-30 min). The main etiologic agents can be diagnosed within the first hours after the onset of symptoms with antigen detection techniques. Given the simplicity and swiftness of their implementation and with which results can be obtained and interpreted, some of these rapid diagnostic tests may also be used as “point-of care tests” (POCT) with the subsequent benefits for the patient, who may receive the diagnosis and, depending on the result, the treatment in one single consultation. 

What are the main factors causing respiratory tract infections?

Upper respiratory tract infections are primarily caused by viruses, accounting for 70% to 80% of cases. These include rhinoviruses, coronaviruses, adenoviruses, influenza and parainfluenza viruses, respiratory syncytial virus, enteroviruses, and coxsackieviruses. Bacterial infections contribute to the remaining 20% to 30%.

Lower respiratory tract infections result from microbial infections, including viruses, bacteria, mycoplasma, chlamydia, and Legionella. These infections represent the most common types of infectious diseases.

Medlere's solutions for respiratory infections

To combat rise of acute respiratory infections, Medlere provides rapid quantitative tests for respiratory infections basing on immunofluorescence technology, which delivers rapid and accurate results within minutes.

•  RSV (Respiratory Syncytial Virus)

•  ADV (Adenovirus)

•  Influenza A/B

•  SARS-CoV-2

•  SARS-CoV-2/Influenza A/B

•  Mycoplasma Pneumoniae

The Clinical Significance of Respiratory Infections Testing

1. Respiratory Syncytial Virus (RSV)

RSV belongs to the paramyxovirus family, Pneumovirus genus, and is generally believed to have only one serotype. It primarily invades the epithelial tissues of the upper respiratory tract, causing necrotizing inflammation that can lead to severe bronchiolitis and pneumonia, especially in breastfed infants and young children.

It is a major influenza virus, with regional respiratory pathogen surveillance in some areas showing RSV positivity rates ranging from 11.58% to 36%. The disease is highly contagious, with a high infection rate in the population, affecting approximately 90% of adults. Although antibodies with neutralizing and complement-binding capabilities are produced after RSV infection, reinfection remains common. Anti-respiratory syncytial virus (RSV) IgM antibodies can appear as early as one week after the onset of symptoms and may persist for 2-3 months.

2. Adenovirus

Adenovirus is a non-enveloped icosahedral DNA virus, and it can be transmitted between individuals through aerosols or contaminated objects. Approximately 6% of respiratory tract infections worldwide are caused by adenovirus.

Its main pathogenic effects include respiratory tract infections, epidemic conjunctivitis (commonly known as 'pink eye'), viral gastroenteritis, acute hemorrhagic cystitis, among others, with respiratory infections and 'pink eye' being the most common. In the initial days after infection, the virus is most abundant in excretions. Anti-adenovirus specific IgM antibodies can appear as early as one week after the onset of symptoms and may persist for 2-3 months.

Influenza Virus

Influenza primarily prevails during the cold seasons, with an incubation period of 1 to 5 days. Influenza viruses belong to the Orthomyxovirus family and are classified into three types: Influenza A (H1N1, H3N2), Influenza B, and Influenza C. These are commonly referred to as Influenza A, Influenza B, and Influenza C. Due to the high genetic variability of influenza viruses, a single infection does not confer lifelong immunity. For high-risk individuals (those with weakened immunity or the elderly), immunization with relevant virus strains can be administered at the beginning of the influenza season, but this provides protection only against the specific subtypes used. Anti-influenza specific IgM antibodies can appear as early as one week after the onset of symptoms and may persist for 2-3 months.

3. Influenza A Virus (H1N1, H3N2)

Influenza A has a broad host range and can infect various animals, including pigs, horses, dogs, poultry, seals, and more. It has also caused global pandemics in humans on multiple occasions. Currently, the main subtypes of Influenza A virus that infect humans are H1N1 and H3N2. Symptoms of Influenza A H1N1 are similar to those of the common cold, with patients experiencing fever, cough, fatigue, and loss of appetite. Reports from the 2009 outbreak in the United States highlighted cases presenting with sudden onset fever, cough, muscle pain, and fatigue. Some patients also reported symptoms such as diarrhea and vomiting. Other symptoms may include fever, cough, sore throat, body aches, headache, fatigue, malaise, loss of appetite, chills, and fatigue. Some individuals may also experience diarrhea or vomiting, muscle pain or fatigue, and red eyes.

4. Influenza B Virus

It usually has a low pathogenicity, occasionally causing localized outbreaks but generally not leading to global pandemics. It is the pathogen responsible for influenza and can result in severe complications in patients with underlying pathology. Due to its tendency to be confused with other respiratory diseases, clinical diagnosis during outbreaks can be challenging. Therefore, laboratory diagnosis becomes crucial.

The onset of illness typically presents with common flu symptoms such as a sudden onset, cough, sore throat accompanied by fever, headache, muscle pain, and discomfort. Symptoms progress, leading to high fever, rapid breathing, cyanosis, paroxysmal cough, and minimal hemoptysis, although it may be blood-streaked.

5. Mycoplasma pneumoniae

Mycoplasma is currently known as one of the smallest self-replicating cells, lacking a rigid cell wall (cell wall defect), rendering antibiotics targeting cell walls essentially ineffective. There are currently 12 recognized species of Mycoplasma in humans. Mycoplasma pneumoniae can cause atypical pneumonia and common upper respiratory tract infections. Infection can occur through aerosols, with humans being the sole host for this pathogen.

Pathological changes in Mycoplasma pneumonia primarily involve interstitial pneumonia, sometimes progressing to bronchopneumonia, termed primary atypical pneumonia. Transmission primarily occurs through droplets, with an incubation period of 2 to 3 weeks, and adolescents having the highest incidence. Clinical symptoms are generally mild, with some cases being entirely asymptomatic or presenting only with common respiratory symptoms such as headache, sore throat, fever, and cough. Rare reports of fatalities exist. Infections can occur throughout the year but are more common in the fall and winter. Additionally, in some cases, pharyngitis and mild ear diseases may occur, but most infections are asymptomatic. Recurrent infections are also possible. Histological studies reveal that Mycoplasma pneumoniae adheres to the epithelial cells of the trachea, bronchi, and bronchioles.

After Mycoplasma pneumoniae infection, IgM and IgA antibodies appear within a week, with an increase in IgG antibody titers several weeks later, persisting for several months. Specific IgM antibodies against Mycoplasma pneumoniae can appear as early as one week after the onset of symptoms and may persist for 3 to 6 months. In differential diagnosis, it is essential to rule out infections caused by Chlamydia pneumoniae, viral pneumonia, psittacosis, and Q fever.

In general, the use of rapid diagnostic tests in the diagnosis of respiratory infections can help to:

• Avoid antibiotics abuse, given that many respiratory infections are of a viral aetiology.

• Ensure the use of suitable anti-viral therapy in specific cases.

• Minimise the use of unnecessary diagnostic tests.

• Reduce the length of hospital stays.

• Permit the swift implementation of isolation measures to limit nosocomial infection, whenever necessary.

Generally speaking, rapid diagnostic tests are useful for the diagnosis of many respiratory infections, facilitating a better approach to infection in all its aspects. Currently, rapid diagnostic tests for detecting antigens can be used as POCTs. Improvements in terms of the simplicity of sample processing and in the interpretation of results would seem to make it likely that in the near future the use of rapid diagnostic tests as POCT for the diagnosis of respiratory infections will become more widespread.

#Respiratory infection #Diagnosis #POCT