Influenza infection
History and exam
Key diagnostic factors
common
winter season
current influenza outbreak
Suspicion for seasonal influenza should be high if there is a documented outbreak in the community. During the influenza season, the Centers for Disease Control and Prevention (CDC) publishes weekly updates online that summarize information about influenza activity. CDC: FluView - weekly influenza surveillance report Opens in new window
unvaccinated
Patients should be asked whether they receive the seasonal influenza vaccine every year. Healthy adults vaccinated with intramuscular inactivated vaccine have a reduced probability of influenza A or B infection and influenza-like illness, although the absolute effect may be modest.[41][61][62] Vaccination in healthy children (with live attenuated vaccine or inactivated vaccine) can reduce influenza and influenza-like illness; the effect varies across populations studied.[43]
fever with cough
Studies in older patients have shown the presence of an acute onset of fever and cough to have a positive predictive value of only 30% to 53% for seasonal influenza in nonhospitalized and hospitalized patients, respectively.[97][98]
A study of vaccinated older people with chronic lung disease reported that cough was not predictive of laboratory-confirmed influenza virus infection, although having both fever or feverishness and myalgia had a positive predictive value of 41%.[99]
Cough and fever may be less prominent symptoms in young children.[96]
If there is an exacerbation of fever and cough with purulent sputum and dyspnea, a secondary bacterial pneumonia should be suspected.
Secondary bacterial pneumonia is an important complication of influenza and contributes to approximately 25% of all influenza-associated deaths.[100]
Other diagnostic factors
common
sore throat
Oropharyngeal symptoms other than sore throat with associated hyperemia are not common.
Risk factors
strong
age ≥65 years
Compared with young, healthy adults, people ages ≥65 years are at greater risk of serious complications from influenza, and are more likely to have comorbid conditions that may be exacerbated by influenza infection. It is estimated that 90% of seasonal influenza-related deaths and more than 60% of seasonal influenza-related hospitalizations in the US each year occur in people ≥65 years.[14][15] Influenza can be a very serious disease when immune defenses become weaker with age. This age also brings a greater likelihood of comorbid conditions that may be exacerbated with influenza infection.[16]
age 6-59 months
Although children with chronic medical conditions such as pulmonary, renal, or cardiac disease have a high risk of complications of influenza, otherwise healthy children are at risk simply because of their age. Children ages <5 years are more likely to be hospitalized than older children; those ages <2 years are at elevated risk of complications attributable to influenza.[17]
chronic cardiovascular or respiratory conditions
In patients with moderate or severe COPD, the presence of any virus in upper airway secretions is strongly associated with the development of COPD exacerbations. These data support the causative role of viruses in triggering COPD exacerbations in the community.[18][19]
In older populations, vaccination against seasonal influenza is associated with reductions in the risk of hospitalization for heart disease, cerebrovascular disease, and pneumonia or influenza, as well as the risk of death from all causes during influenza seasons. These findings highlight the benefits of vaccination and support efforts to increase the rates of vaccination among older people.[19][20][21]
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diabetes
People with diabetes are at greater risk of complications due to their underlying disease.[22] Diabetes confers a 5% to 12% increase in mortality from seasonal influenza infection, thought to be due to increased risk of metabolic disruption, ketoacidosis, impaired immune response, and increased carrier rates of staphylococci and streptococci.[23]
hemoglobinopathy
Hemoglobinopathies such as sickle cell disease involve abnormalities not just in red blood cells but also in vascular endothelium, white blood cell function, coagulation, and inflammatory response. Routine influenza vaccination is recommended for infection prevention.[24]
immunocompromised status
Infection is the leading cause of morbidity and mortality in immunocompromised patients such as hematopoietic/solid organ transplant recipients and individuals with HIV.[25][26][27] Immunocompromised people are at higher risk of complications from influenza infection and should be vaccinated with any licensed, recommended, age-appropriate inactivated vaccine. Inactivated vaccines should be used with caution in severely immunocompromised patients (e.g., patients receiving chemotherapy, radiation therapy, or other immunosuppressive therapy, including high-dose corticosteroids), as there may be a reduced response to vaccination. However, adjuvanted vaccine has been shown to be safe and immunogenic in the transplant population.[28] Intranasal live-attenuated vaccine is contraindicated in immunosuppressed or immunocompromised patients. Inactivated influenza virus vaccine is also preferred over live virus vaccine for household members, healthcare workers, and others coming into close contact with severely immunosuppressed people requiring care in a protected environment.[29]
chronic kidney disease (CKD)
Patients with CKD are at increased risk of influenza complications.[16] Influenza vaccine is currently recommended for patients with CKD by the Advisory Committee on Immunization Practices of the Centers for Disease Control and Prevention (note that CKD is a precaution for the use of the live attenuated influenza vaccine).[30] In observational studies, influenza vaccination is associated with decreased risk of influenza-related hospitalizations, deaths, and physician visits.[31]
pregnancy
Immune, respiratory, and cardiovascular changes make pregnant women more prone to severe illness from influenza.[32] Pregnant women with influenza have a greater risk of maternal morbidity as well as obstetric complications such as preterm labor and delivery.[33][34][35] Pregnant women may receive any licensed, recommended, age-appropriate inactivated vaccine; the live attenuated influenza vaccine should not be used during pregnancy.[30][33] See Primary prevention.
caregivers and household contacts of high-risk groups
The goal is to prevent transmission of the virus to a high-risk population.
Inactivated influenza virus vaccine is preferred over live virus vaccine for household members, healthcare workers, and others coming in close contact with severely immunosuppressed people requiring care in a protected environment.
healthcare workers
Healthcare workers play an important role in protecting public health. The Advisory Committee on Immunization Practices of the Centers for Disease Control and Prevention recommends that all healthcare workers receive an annual influenza vaccination to limit the spread of infection.[36] Inactivated influenza virus vaccine is preferred over live virus vaccine for household members, healthcare workers, and others coming in close contact with severely immunosuppressed people requiring care in a protected environment.
As a vaccinated healthcare worker, there is protection for family at home as well as patients at work from possible influenza transmission. Influenza outbreaks in hospitals and long-term care facilities have been attributed to low vaccination rates among healthcare professionals.[37]
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