Interpreting Results

With its high sensitivity and same- to next-day turn-around time, xTAG RVP can provide useful information for timely clinical decision-making.  See Interpretation of TDAS RVP-I Outputs and Retest Recommendations sections of the package insert.

Important results to watch for:

• Positive for non-specific influenza A but not for seasonal H1 or H3 subtype: possible 2009 Influenza A/H1N1 (Swine Flu)
• Co-infections, particularly in immunocompromised or immunosuppressed patients: may have more serious course
• Any reportable infectious disease: see the CDC’s site for the most up-to-date national list, and your local public health authorities for local reporting requirements

Clinical importance of various respiratory virus types

Influenza viruses

• Each year, about one in four people in the general population will contract an influenza infection but many opt not to see their physicians.¹
• Seasonal outbreaks are most commonly caused by influenza A; influenza B is found in most but not all years and is less likely to be the source of the season’s main outbreak.¹
• Occasionally, influenza A subtypes from other mammals (e.g., pigs) or birds acquire the ability to infect humans; this can result in a pandemic strain. There were well-documented influenza pandemics in 1890, 1900, 1918, 1957, and 1968.¹
• Annually in the United States, there are an estimated 200,000 hospitalizations for seasonal influenza and 36,000 flu-related deaths.^{2, 3}
• Antivirals such as oseltamivir or zanamivir may be effective if started within a 48-hour window of symptom onset.⁴
  
  

Respiratory syncytial virus (RSV)

• RSV follows a distinctive outbreak pattern in temperate regions, where each winter it infects about 50% of babies. The following year, the other half of the infant population will become infected. In the tropics, there is no defined RSV season and infections occur year-round.¹
• About 70% of infants will have an RSV infection within the first year of life; most children have been infected at least once by age 2.⁵
• The initial infection is the most severe, causing lower respiratory tract disease (e.g., bronchiolitis) in 20-30% of affected infants.⁵
• RSV infections can also occur in adults, and are more serious in individuals who are immunocompromised or immunosuppressed.¹ In highly immunosuppressed transplant patients, RSV infection may necessitate cessation or modification of anti-rejection therapy.⁴
• Aerosolized ribavirin can be used for treatment of RSV infection in high-risk patients (e.g., immunocompromised or severely ill infants).⁴
  
  

Parainfluenzas

• The parainfluenzas are largely childhood viruses, and are the second most important cause (after RSV) of pediatric hospital admissions for respiratory disease, and are the leading cause of croup.¹
• Most adult infections are re-infections after previous childhood exposure. In most cases, these cause only upper respiratory symptoms.¹
• The seriousness of a parainfluenza infection’s course depends largely on the patient’s immune status. In immunosuppressed individuals, especially transplant
• patients, parainfluenza infection can often lead to pneumonia.¹
• Reliable identification of parainfluenza virus as the causative agent is crucial for infection control in the inpatient setting, where patients with differing immune competence may be in close proximity.¹
  
  

Human metapneumovirus (hMPV)

• hMPV was first identified in 2001 and is now ranked as the second most common cause (after RSV) of lower respiratory tract illness in children.⁶
• Most children have been infected with hMPV by age 5, but infections can occur in any age group.¹
• hMPV is ubiquitous worldwide.⁶ Outbreaks in temperate climates most often occur in winter/spring, often overlapping or following the winter RSV outbreak, but sporadic infections also occur year-round.¹Immunocompromised patients have significant rates of infection;³ co-infection with hMPV and RSV is associated with more a severe disease course in this population.⁷
  
  

Rhinovirus

• Although rhinovirus infection is not normally thought of as very serious, it often exists as a mixed infection with a more sever course.¹
• The addition of a rhinovirus co-infection to a RSV infection can lead to more severe illness and is more likely to cause bronchiolitis than RSV infection alone.⁵
• Rhinovirus infection plays an important role in exacerbations of asthma and chronic obstructive pulmonary disease (COPD).¹
• In the elderly, rhinovirus infections often have a more sever course than in younger patients. About one in five elderly patients with a rhinovirus infection will be bedridden due to symptoms, and development of lower respiratory complications is common.⁸
  
  

Adenovirus

• Some strains of adenovirus are endemic, especially, especially among children, and are generally not associated with severe disease in otherwise healthy individuals.⁹
• Adenovirus often causes disseminated and potentially life-threatening disease in immunocompromised or immunosuppressed individuals.⁹
• The best-described outbreaks of adenovirus have occurred in closed environments, notably military training facilities.¹⁰
• Some forms can cause community outbreaks; fatalities have been observed.¹¹

 References:

1. Carman WF, Mahony JB. JCV 2007 (Suppl 1) S5-S10.
2. Centers for Disease Control and Prevention Q&A, available online at http://www.cdc.gov/flu/about/qa/hospital.htm
3. Centers for Disease Control and Prevention Q&A, available online at http://www.cdc.gov/flu/about/disease/us_flu-related_deaths.htm
4. Mahony JB. JCV 2007 (Suppl 1) S36-S38.
5. Templeton KE. JCV 2007 (Suppl 1) S2-S4.
6. Maranich A et al. eMedicine fact sheet, available online at http://emedicine.medscape.com/article/237691-overview
7. Dr Michael Ison, personal communication.
8. Nicholson KG et al. BMJ 1996;313:1119-1123.
9. Lenaerts L et al. Rev Med Virol 2008;18:357-374.
10. MMWR Weekly, July 17, 1998/47(27);567-570.
11. Mitchell LS et al. Pediatr Infect Dis J 2000;19:996-1000.