Viral infections commonly affect the upper or lower respiratory tracts with different clinical syndromes such as common cold, croup, and bronchiolitis (1). Influenza-like illness (ILI), also known as an acute respiratory infection is a medical diagnosis of possible influenza or other illness causing a set of common symptoms such as fever > 38 °C or at least two acute respiratory symptoms, cough and/or sore throat, nasal obstruction/rhinorrhea (2). Viral agents cause these infections, including influenza virus, human parainfluenza virus (HPIV), respiratory syncytial virus (RSV), rhinovirus, coronavirus, adenovirus, and metapneumovirus.
Acute viral respiratory tract infection is a major cause of mortality in developing countries. Death can result either from a viral infection or a bacterial superinfection, especially in high-risk patients. Even though these viral diseases are self-limited, they can cause a variety of complications in children, the elderly, pregnant women, immunocompromised patients and those with chronic renal disease, heart failure, or asthma (1-4).
The Center for Disease Control and Prevention confirmed the definition of influenza-like illness, so the patients in accordance with this definition are infected with influenza. However, several studies showed that respiratory viruses other than influenza virus might be responsible for similar condition (5).
The influenza virus is responsible for annual epidemics, which is characterized by a sudden increase in febrile respiratory illness and the absence from schools and workplaces. Seasonal influenza viruses with variable clinical pictures are common during the fall and winter. Its differentiation from other agents is important in clinical practice because it has specific antiviral treatment. Also, the identification of influenza virus is crucial as appropriate infection control practices play a major role in outbreak prevention. Influenza virus outbreaks in hospitals can be devastating, especially for immunocompromised patients who are highly susceptible to life-threatening influenza virus infection.
Human parainfluenza viruses include four serotypes that infect humans. Their route of transmission and pathogenesis are similar to that of the influenza viruses. Human parainfluenza viruses can cause mild upper respiratory tract infections (URTIs), pharyngitis, and tracheobronchitis (5, 6). However, HPIV1 and HPIV3 are associated with mild URTI, and croup in children and infrequently, lower respiratory tract infections (LRTI), which occur predominantly in the fall. Human parainfluenza virus type 2 is generally associated with LRTI. Human parainfluenza virus type 4, which is generally associated with mild URTI, is comprised of the least common virus of this group. Overall, HPIVs cause 15 to 30% of non-bacterial respiratory disease in children requiring hospitalization (6).
Respiratory syncytial virus (RSV) subtypes A and B are major causes of bronchiolitis and pneumonia in infants. Most infections occur between late fall and early spring, with a peak prevalence in the winter. The initiation of the disease is often with rhinitis, which develops severe respiratory symptoms. However, RSV-A is more severe than RSV-B (7, 8).
Respiratory infections caused by the mentioned viruses usually present with clinical features that are really difficult to distinguish (8). The diagnosis is made by the detection of pathogens by polymerase chain reaction (PCR), cell culture, or serologic tests. More rapid diagnostic tests should be reserved when the pathogen-specific diagnosis is important for clinical management. The increased sensitivity of PCR over conventional methods like cell culture and serology makes it more practical for the diagnosis of respiratory viral infections (9). However, organism-specific RT-PCR assays, which require separate amplification of every single virus, are resource- and labor intensive as well as time-consuming (10).
The Multiplex RT-PCR method is rapid, sensitive, specific, and more cost-effective than alternative methods such as culture (11). The Multiplex RT-PCR, which is both highly sensitive and specific for each virus and detection of co-infection in clinical samples, can be used in studies of viral respiratory infections in both surveillance and laboratory diagnostic tests (12).
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