30 HOW TO TREAT : INFLUENZA
30 HOW TO TREAT : INFLUENZA
14 MARCH 2025 ausdoc . com . au
PAGE 27 Pregnant patients with relevant comorbidities are at an even greater risk of complications from influenza than their non-pregnant counterparts , with risk rising across trimesters and up to four weeks postpartum . 23 , 37 Maternal influenza may increase risk of preterm birth , low birthweight , birth of a small-for-gestational-age infant , and fetal loss though fetal effects appear more likely to occur in the
23 , 38 severely unwell .
DIAGNOSIS AND INVESTIGATIONS
DIAGNOSTIC testing for influenza is warranted where the results influence either clinical management decisions ( such as the initiation of antivirals or antibiotics , further diagnostic evaluation , prophylaxis provision to high-risk contacts , or infection control interventions ) or public health actions , such as outbreak management
23 , 29 interventions .
Do not exclude the possibility of influenza in vaccinated patients as vaccine effectiveness varies with age , host immune status , and the match between circulating and vaccine virus strains . Note that influenza vaccine effectiveness ranges from very low to about 40-60 % in
16 , 39 well-matched seasons .
When influenza viruses are the predominant respiratory viruses in the community , clinical diagnosis of uncomplicated infection is usually reliable . In adults under 65 who present with an acute febrile respiratory illness , are not at high risk for influenza complications and do not require hospital admission , and in whom COVID-19 has been excluded , a clinical diagnosis of influenza may be made based on clinical manifestations . 16 The WHO global influenza surveillance standards define the surveillance case definition for ILI as an acute respiratory infection with measured fever of 38 ° C or greater and cough , with onset within the past 10 days . 40 A study of 1581 patients presenting to ED who received a nasopharyngeal swab followed by PCR testing for respiratory viruses demonstrated that the best predictors for laboratory-confirmed influenza , regardless of age group , included cough , fever , rhinorrhoea and myalgias . 41 Consider a diagnosis of influenza in those listed in box 2 .
During co-circulation of influenza A and B viruses and SARS- CoV-2 in the community , testing using a multiplex assay can help distinguish between influenza and COVID-19 or identify co-infection . 16 A positive test result for influenza alone does not rule out SARS-CoV-2 co-infection when both viruses are present in the community . This is important because COVID-19 is associated with greater illness severity , complication rate , length of hospital stay , ICU admission and in-hospital mortality compared with influenza . COVID-19 may warrant therapeutics
16 , 42 not used for influenza infection .
The most useful tests for the diagnosis of influenza are rapid molecular assays , such as nucleic acid amplification tests ( NAATs ), for example , PCR , of nose or throat swab samples . 29 Antigen detection assays , including rapid influenza tests that yield results in about 10 minutes , and immunofluorescence
Box 2 . Groups in whom to consider a diagnosis of influenza *
• During influenza activity ( acute onset of respiratory symptoms , with or without fever [ all ages ]): — Pneumonia ( all ages ). — Acute exacerbation of chronic lung disease ( eg , COPD , asthma ), with or without fever ( all ages ). — Fever without obvious source ( infants , young children ). — New-onset neurological signs and symptoms ( eg , seizures , altered mental status ), with or without fever
( infants , young children ). — Exacerbation or new onset of cardiovascular events ( eg , heart failure , MI or ischaemia , CVA in adults ) or altered mental status , with or without fever ( all ages ). — Severe , complicated , or progressive acute respiratory illness , without an alternative diagnosis ( all ages ). — Hospitalised patients who develop new onset of acute respiratory symptoms , with or without fever
( all ages ).
• Year-round ( acute onset of respiratory symptoms , with or without fever , especially those at high risk for influenza complications who are epidemiologically linked to recent influenza cases or outbreaks [ all ages ]): — Healthcare personnel caring for influenza patients . — Healthcare personnel , residents , or visitors to an institution experiencing an influenza outbreak . — Close contacts of persons with suspected influenza ( household or a congregate setting , such as daycare , school , or healthcare facility ). — Returned travellers from areas where influenza viruses may be circulating . — Organised tour group participants . — Participants of mass gatherings such as sporting events , festivals , conferences , worship services , camps , cruise ships . * Consider a diagnosis of influenza regardless of current season influenza vaccination because influenza vaccine effectiveness is variable . Adapted from Infectious Diseases Society of America Influenza Clinical Guidelines 2018 23
assays , have low to moderate sensitivity in detecting influenza viruses in respiratory specimens and have a potential risk of false-negative results . 16 NAATs also provide opportunities to identify the strain of influenza and are often multiplex , targeting a panel of common respiratory pathogens such as influenza , respiratory syncytial virus , parainfluenzavirus , and coronaviruses , including SARS -CoV- 2 , an advantage in the ill hospitalised patient and during outbreaks of other respiratory pathogens . 7
Collect respiratory specimens as close to illness onset as possible . In the critically ill , testing of endotracheal aspirate or bronchoalveolar lavage fluid may be required as viral replication can be prolonged in the lower respiratory tract ; a negative result of upper respiratory specimens may be falsely reassuring . 16 When collecting samples from patients with suspected influenza use infection control precautions . 29
The sensitivity of virus detection by NAATs is highest during the first few days of illness , usually higher in children than in adults , and higher with nasopharyngeal or nasal swabs than with throat specimens . The positive predictive value of the tests is greatest during peak influenza activity , and the negative predictive value is greatest during low activity or outside the influenza season .
When evaluating the results of influenza testing in returning travellers , consider the influenza activity at their point of departure . 16
Viral culture results take 3-10 days , so do not provide timely results for clinical management and should not be used for initial or primary diagnosis of influenza . Do not use serological testing routinely because of the need for collection of acute and convalescent serum specimens for accurate interpretation . 7 , 16
In hospitalised patients with suspected influenza , the use of empirical antivirals and isolation and implementation of infection prevention and control measures should not be delayed awaiting the results of molecular assays . 7 , 29
Other investigations are of limited value . Mild leucopenia is seen in influenza , while a white blood cell count above 15x10 9 / L suggests a secondary bacterial component in influenzal pneumonia . 7
MANAGEMENT
INFLUENZA often requires only symptomatic management . Encourage patients to maintain adequate hydration and use paracetamol or NSAIDs to ameliorate fever , headache and myalgia . Avoid aspirin in those with suspected or confirmed influenza , especially young children and adolescents , because of the association between aspirin and the risk of Reye ’ s syndrome . 16
Antiviral therapy has been limited by the few treatment options available , the short duration of symptoms in uncomplicated influenza , and the emergence of drug resistance in influenza viral strains . For example , previously influenza A infection could be treated with M 2 channel blockers such as amantadine ; however , widespread resistance means these antivirals are no longer viable options . 7
The mainstay of influenza antivirals are the neuraminidase inhibitors ( NAIs ). These inhibit the influenza surface enzyme neuraminidase and thus limit the egress of influenza virus from the infected cell . 7 Treatment of influenza with an NAI , such as oseltamivir or zanamivir , has
Figure 6 . Cervical lymphadenopathy .
been associated with fewer complications ( including bronchitis , otitis media , and pneumonia ), hospital admissions and mortality in systematic reviews of observational studies . These studies included people at high risk of severe influenza or mortality from influenza . 23 , 29 Other studies that largely recruited healthy , low-risk adults did not demonstrate such benefits , though these studies were underpowered to detect important outcomes such as hospitalisation and mortality .
23 , 29
In otherwise healthy adults at low risk of complications , treatment with NAIs , when initiated within 48 hours of symptom onset , reduces the duration of influenza symptoms by 0.6-1 day . This limited benefit should be balanced against the potential adverse effects of NAIs , including nausea , vomiting , headaches and
23 , 29 neuropsychiatric events .
Offer NAIs to those who need to be admitted to hospital for management of influenza , have established complications or have moderate to high severity community-acquired pneumonia during the influenza season . Consider treatment for individuals at higher risk of poor outcomes from influenza ( see table 3 ) or in those with progressive disease who do not require hospitalisation . Observational studies in hospitalised patients indicate that the greatest clinical benefit occurs when antiviral treatment is started close to illness onset or at hospital admission when compared with no treatment or later treatment initiation , so consider initiation even beyond two days from illness onset . Initiate treatment without waiting for test results . Consider a longer duration of NAI therapy , up to 10 days , in patients with severe influenza or in those who are
16 , 29 immunocompromised .
Discuss the harms and benefits of NAIs in pregnant women and the early postpartum period because of the higher risk of poor outcomes from influenza in pregnancy . 29 Oseltamivir and zanamivir are listed as category B1 medications . From the limited information available , these are considered safe during pregnancy and breastfeeding as maternal