Influenza viruses

---

---

 

There are three group of influenza viruses.

Influenza A and B are the most important groups.

 

1.Type A is the main causes of seasonal outbreak and epidemics.

   It is also associated with pandemics.

 

2. Type B causes sporadic cases.

 

3. Influenza C is associated with mild upper respiratory infection and is uncommon.

 

Transmission

Person to person transmission is through respiratory route.

 

Incubation period

The incubation period is short (1 to 3 days)

Infectious period starts 1 day before the onset of illness  and lasts for 3 to 5 days after onset.

---

Clinical presentation

---

 

Mild infection is common.

Fever and malaise.

Running nose

Headache, myalgia.

Generalized weakness.

In the majority of patients clinical improvement can be seen after 3 days.

Some may experience fatigue for several weeks.

 

Influenza A

It is the causes of the major pandemics.

Genetic drift and shift are common with influenza A.

Fever, headache, easy fatigability are common

Cough, and later become productive of sputum.

Myalgia and arthralgia are common.

Followed by signs and symptoms of pneumonia

Cough, fever, tachypnoea, tachycardia

Signs of consolidations

Secondary bacterial pneumonia is common in the elderly patients.

Mortality is high in patients who develop primary or secondary pneumonia.

 

Influenza B

It is mild compared to Influenza A.

It is common in children and young adults.

 

Complications of Influenza

Ø      Viral pneumonia

Ø      Secondary bacterial pneumonia

Ø      Encephalitis

Ø      Reye’s syndrome

---

Investigation

---

Diagnostic tests

Respiratory secretions- IF, PCR, virus isolation

Serum for CFT- Convalescent blood sample is required for CFT.

Influenza RNA PCR

There are some point of care tests. They are less sensitive however they are helpful to identify infected patient in order to implement  proper infection control measures.

 

---

Treatment 

---

 

It is a self-limiting illness.

 

Community care

Elderly patients presented with influenza like illness should be treated with Zanamivir if they present within 48 hours of onset.

Antiviral therapy is not required to treat Immunocompetent person unless they develop severe infection.

 

Care to Hospitalised patients

Respiratory isolation is essential to control person to person transmission.

Antiviral therapy is effective if patients can take them within the first 48 hours of illness.

Zanamivir or Oseltamivir are indicated for patients with severe illness, or for patients at risk of severe illness or complications.

Rimanatadine or Amantadine may be used but they are only effective against Influenza A.

 

Aspirin should not be used in children who are suspected to have infection with influenza.

---

Prevention 

---

 

Eeffective vaccines is available.

The vaccine contains antigens from one influenza B strain and two Influenza A strains. Annual vaccination is recommended to elderly patients and to others with risk factors that are associated with high mortalities (cardiac disease, chronic respiratory disorder, HIV infected patients or diabetic mellitus).

Antiviral can be used as post-exposure prophylaxis.

Outbreaks in nursing homes can be prevented by immunisation and/or antivirals.

---

---