Influenza - Guidelines for Clinical Management of Adult Patients with

Publication: 24/12/2010  --
Last review: 06/01/2020  
Next review: 06/01/2023  
Clinical Guideline
ID: 2356 
Approved By: Trust Clinical Guidelines Group 
Copyright© Leeds Teaching Hospitals NHS Trust 2020  


This Clinical Guideline is intended for use by healthcare professionals within Leeds unless otherwise stated.
For healthcare professionals in other trusts, please ensure that you consult relevant local and national guidance.

2018-19 Guidelines for Clinical Management of Adults with Influenza

Incubation and infective period

The incubation period prior to the onset of symptoms is 2 – 4 days (range 1 – 7).  The period of infectivity is from a day before onset of symptoms to 5 days after (7 days in children).

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Clinical features

NB. The spectrum of clinical disease associated with a new influenza A subtype (i.e. a pandemic strain) may differ from that described below for interpandemic influenza.

Uncomplicated influenza

The illness typically presents as an abrupt onset of fever accompanied by a range of other symptoms:

  • cough (85%)
  • malaise (80%)
  • chills (70%)
  • headache (65%)
  • anorexia (60%)
  • coryzal symptoms (60%)
  • myalgia (53%)
  • sore throat (50%)

The cough is generally dry although in up to 40% of cases it may be productive. A productive cough together with chest tightness and substernal soreness is more common in patients with underlying chronic lung disease. Myalgia affects mainly the back and limbs. Gastrointestinal symptoms such as vomiting and diarrhoea are uncommon (<10%) in adults. Abdominal pain is rare.
Clinical findings include a toxic appearance in the initial stages, hot and moist skin, a flushed face, injected eyes and hyperaemic mucous membranes around the nose and pharynx. Tender cervical lymphadenopathy is found in a minority (10%) of cases. Wheezing or lung crackles are recognised findings (10%) more commonly noted in patients with coexisting chronic lung disease.

In uncomplicated infection, the illness usually resolves in 7 days although cough, malaise and lassitude may persist for weeks.

Complications of influenza





Acute bronchitis


More common in elderly and those with chronic medical conditions.

Primary viral pneumonia


Onset within 48 hours of start of fever.

Secondary bacterial pneumonia


Typically occurs 4 – 5 days after onset of illness.



In young children



Children, can be severe


ECG abnormalities


Non-specific T wave and rhythm changes, ST segment deviation. Mostly not associated with cardiac symptoms.










Occurs during early convalescence

Myoglobinuria and renal failure



Central Nervous System

Encephalitis/ encephalopathy


Occurs within first week of illness. More common in children.

Transverse myelitis

Very rare


Guillian-Barre syndrome

Very rare



Otitis media

Uncommon in adults, very common in children


Toxic shock syndrome




Very rare


Influenza-related pneumonia

The incidence of pneumonia (defined as a combination of respiratory symptoms and signs supported by CXR changes consistent with infection) complicating influenza varies from 2% to 38%, and is dependent on viral and host factors.

Pneumonia generally occurs more frequently and with greater severity in patients with pre-existing chronic cardiac and respiratory conditions. Symptoms and signs are indistinguishable from pneumonia related to other viral and bacterial pathogens.

Two main types of influenza-related pneumonia are recognised; the uncommon but more severe primary viral pneumonia and the more common secondary bacterial pneumonia.

Primary viral pneumonia

Patients with primary viral pneumonia typically become breathless within the first 48 hours of onset of fever. An initially dry cough may become productive of blood-stained sputum. Cyanosis, tachypnoea, bilateral crepitations and wheeze on chest examination and leucocytosis are usual. The commonest chest radiographic abnormality is of bilateral interstitial infiltrates predominantly in the mid-zones, although focal consolidation is also seen. Rapid clinical deterioration with respiratory failure may ensue. The mortality in hospitalised patients is high (>40%) despite maximum supportive treatment. In the majority of fatal cases, death occurs within 7 days of hospital admission.

Secondary bacterial pneumonia

Secondary bacterial pneumonia is more common than primary viral pneumonia. Typically, symptoms and signs of pneumonia develop during the early convalescent period (4 – 5 days from onset of initial symptoms). In others, symptoms of pneumonia blend in with the initial symptoms of influenza. Chest radiography usually demonstrates a lobar pattern of consolidation. Mortality rate ranges from 7 - 24%.
The spectrum of pathogens implicated includes Streptococcus pneumoniae, Staphylococcus aureus, Haemophilus influenzae and Groups A, C and G beta-haemolytic streptococci. Secondary staphylococcal pneumonia is associated with a higher incidence of lung abscess formation and carries a poorer prognosis (mortality 47%) compared to non-staphylococcal pneumonias (mortality16%).

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Management of adults with influenza

Uncomplicated influenza

Patients with uncomplicated influenza infection would be expected to make a full recovery and do not require hospital care.  In uncomplicated infection, the illness usually resolves in 7 days although cough, malaise and lassitude may persist for weeks.

Patients with exacerbation of pre-existing co-morbid medical conditions should be managed according to best practice for that condition.

Influenza-related pneumonia

Severity can be assessed by CURB-65 score (see below) 

However, patients with bilateral lung infiltrates on CXR consistent with primary viral pneumonia should be managed as having severe pneumonia regardless of CURB-65 score.

CURB-65 score
Score 1 point for each feature present:
Confusion (Mental Test Score of ≤ 8, or new disorientation in person, place or time)
Urea > 7 mmol/l
Respiratory rate ≥ 30/min
Blood pressure (SBP < 90mmHg or DBP ≤ 60mmHg)
Age ≥ 65 years

CURB-65 score of 3, 4 or 5 are at high risk of death - manage as severe pneumonia.

CURB-65 score of 2 are at increased risk of death - consider for short stay inpatient treatment or hospital supervised outpatient treatment.

CURB-65 score of 0 or 1 are at low risk of death - treat as having non-severe pneumonia and may be suitable for home treatment.

High Dependency or Intensive Care Unit transfer

Patients with primary viral pneumonia or a CURB-65 score of 4 or 5 should be considered for HDU/ICU transfer if:

  • persisting hypoxia with PaO2 <8Kpa despite maximal oxygen administration
  • progressive increase in PaCO2
  • severe acidosis (pH<7.26)
  • septic shock

General Investigations

Full blood count, Urea and electrolytes, Liver function tests, CRP
Chest x-ray
Pulse oximetry
ECG (Patients with cardiac and respiratory complications or co-morbid illnesses).

Microbiological investigations

All suspected cases

  • Rapid/Point-of-care-test (POCT) where available
  • Throat swabs in virus transport medium for respiratory virus PCR (regardless of POCT result)

Severe pneumonia

  • Blood culture (preferably before antibiotic treatment is commenced)
  • Sputum M, C &S
  • Pneumococcal urine antigen (20 mls urine sample)
  • Legionella urine antigen (20 mls urine sample)

Non-severe pneumonia (CURB-65 Score 0, 1 or 2)

  • No routine testing.
  • Sputum M, C & S if poor response to antimicrobials

Antiviral treatment
Uncomplicated influenza in otherwise healthy adults does not require antiviral treatment. Antivirals should be given for patients with severe complications of pneumonia e.g. viral pneumonia. Specific detailed recommendations for antiviral therapy are available HERE (LTHT Internal Link)

Patients who are unable to mount an adequate febrile response eg. the immunocompromised or very elderly, should receive antiviral treatment despite lack of documented fever.

Hospitalised patients who are severely ill, particularly if also immunocompromised, may benefit from antiviral treatment started more than 48 hours from disease onset.

Antibiotic Management of respiratory complications

Bronchial complications without influenza-related pneumonia
Previously well adults with acute bronchitis complicating influenza, in the absence of pneumonia, do not routinely require antibiotics. Antibiotics should be considered in those previously well adults who develop worsening symptoms. Procalcitonin (PCT) can be used in patients without sepsis or proven secondary bacterial infection to reduce the use of unnecessary antibiotics.

Patients at risk of complications should be considered for antibiotics in the presence of lower respiratory features. These include patients who are within the group currently recommended for influenza vaccination.
The preferred choice is Doxycycline electronic Medicines Compendium information on Doxycycline.

Non-severe influenza-related pneumonia
The preferred choice is oral Co-Amoxiclav electronic Medicines Compendium information on Co-Amoxiclav (Amoxicillin-Clavulanate). When oral therapy is contra-indicated, use Co-Amoxiclav electronic Medicines Compendium information on Co-Amoxiclav (Amoxicillin-Clavulanate). Doxycycline electronic Medicines Compendium information on Doxycycline is an alternative in penicillin allergy

Severe influenza-related pneumonia
The preferred choice is Co-Amoxiclav electronic Medicines Compendium information on Co-Amoxiclav (Amoxicillin-Clavulanate) and Clarithromycin electronic Medicines Compendium information on Clarithromycin . Seek Microbiology or Infectious Diseases advice if penicillin allergy.


Record: 2356
Clinical condition:


Target patient group: Adults
Target professional group(s): Pharmacists
Secondary Care Doctors
Secondary Care Nurses
Adapted from:

Evidence base

Not supplied

Approved By

Trust Clinical Guidelines Group

Document history

LHP version 1.0

Related information

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