WHO | Clinical management of human infection with pandemic (H1N1) 2009: revised guidance

Clinical management of human infection with pandemic (H1N1) 2009: revised guidance
Publication date: November 2009

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Summary
This guidance provides updated information for health care providers managing patients with suspected or confirmed pandemic (H1N1) 2009. It incorporates knowledge gained about clinical features of pandemic influenza through international consultations.

Key topics:

risk factors for severe disease
signs and symptoms of progressive disease
diagnosis
treatment, both outpatient and in hospitals, and
clinical care for resource-poor settings.
Highlights
Diagnosis
Uncomplicated influenza can be diagnosed based on signs and symptoms presented by patients when influenza is known to be circulating in a community.

All patients should be advised to return to their health care provider for follow-up if they develop signs or symptoms of progressive disease.

Signs of progressive illness can include:

persistent high fever beyond 3 days
shortness of breath or difficulty in breathing, or turning blue
bloody or coloured sputum, chest pain or low blood pressure
in children, fast or laboured breathing
drowsiness, confusion or severe weakness
dehydration, which can cause dizziness, decreased urine output or lethargy.
Diagnostic testing to confirm the pandemic virus should be prioritized for patients at higher risk for severe illness.

However, clinicians who should not delay treatment of a patient with symptoms of an influenza-like illness to wait for laboratory confirmation of H1N1 virus infection.

Treatment
Mild illness continues to characterize most cases, and basic supportive care (to relieve aches or fever) is sufficient for most people. However, health care providers should give all of their patients guidance on how to recognize signs of progressive illness, and when to seek medical attention.

For pregnant women, WHO advises early antiviral treatment for suspected or confirmed pandemic influenza illness.

Infants and very young children (those under 2 years of age), especially those with underlying conditions, should also be treated with antiviral medication if warning symptoms arise.

In general, antiviral treatment recommendations are:

Patients who have severe or progressive illness should be treated with antiviral medication as soon as possible.
People with mild symptoms but who are at higher risk for severe illness (e.g. pregnant women, infants and young children, and those with chronic lung problems) should start antiviral treatment as soon as possible.
Antiviral treatment is not necessary for people have uncomplicated, or mild, illness and are not in a high risk group for severe illness.
Mothers who are breastfeeding can continue breastfeeding while ill and receiving antiviral treatment.

In hospital settings, health providers should monitor oxygen levels closely and supplement oxygen as needed, following guidelines. When pneumonia is present patients should be treated with both antiviral medication and antibiotics as early as possible.

Advice for how to evaluate and care for severely ill patients in hospital settings is explained.

Resource-poor settings
In health care settings where resources are limited, clinical care should focus on early use of primary health care (by the family doctor or at health clinics, for example) to determine what type of care or treatment is necessary for a patient, and to set priorities for who needs hospital care most urgently. Health care decisions should be based on signs and symptoms of illness, and the level of influenza activity in the local area.

Decentralizing stocks of antiviral medications, even if supplies are limited, is important to reach at-risk groups and disadvantaged populations.

Related links
Clinical features of severe cases of pandemic influenza (see below)

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WHO | Clinical management of human infection with pandemic (H1N1) 2009: revised guidance

Clinical features of severe cases of pandemic influenza
Pandemic (H1N1) 2009 briefing note 13

16 OCTOBER 2009 | GENEVA -- To gather information about the clinical features and management of pandemic influenza, WHO hosted a three-day meeting at the headquarters of the Pan American Health Organization in Washington, DC on 14–16 October. Findings and experiences were presented by around 100 clinicians, scientists, and public health professionals from the Americas, Europe, Asia, Africa, the Middle East and Oceania.

The meeting confirmed that the overwhelming majority of persons worldwide infected with the new H1N1 virus continue to experience uncomplicated influenza-like illness, with full recovery within a week, even without medical treatment.


Clinical management of human infection with pandemic (H1N1) 2009: revised guidance
Pandemic (H1N1) 2009

However, concern is now focused on the clinical course and management of small subsets of patients who rapidly develop very severe progressive pneumonia. In these patients, severe pneumonia is often associated with failure of other organs, or marked worsening of underlying asthma or chronic obstructive airway disease.

Treatment of these patients is difficult and demanding, strongly suggesting that emergency rooms and intensive care units will experience the heaviest burden of patient care during the pandemic.

Primary viral pneumonia is the most common finding in severe cases and a frequent cause of death. Secondary bacterial infections have been found in approximately 30% of fatal cases. Respiratory failure and refractory shock have been the most common causes of death.

Presentations during the meeting explored the pathology of severe disease in detail, with findings supported by work in experimental animals. These findings confirm the ability of the new H1N1 virus to directly cause severe pneumonia.

Clinical picture different from seasonal influenza
Participants who have managed such cases agreed that the clinical picture in severe cases is strikingly different from the disease pattern seen during epidemics of seasonal influenza. While people with certain underlying medical conditions, including pregnancy, are known to be at increased risk, many severe cases occur in previously healthy young people. In these patients, predisposing factors that increase the risk of severe illness are not presently understood, though research is under way.

In severe cases, patients generally begin to deteriorate around 3 to 5 days after symptom onset. Deterioration is rapid, with many patients progressing to respiratory failure within 24 hours, requiring immediate admission to an intensive care unit. Upon admission, most patients need immediate respiratory support with mechanical ventilation. However, some patients do not respond well to conventional ventilatory support, further complicating the treatment.

On the positive side, findings presented during the meeting add to a growing body of evidence that prompt treatment with the antiviral drugs, oseltamivir or zanamivir, reduces the severity of illness and improves the chances of survival. These findings strengthen previous WHO recommendations for early treatment with these drugs for patients who meet treatment criteria, even in the absence of a positive confirmatory test.

In addition to pneumonia directly caused by replication of the virus, evidence shows that pneumonia caused by co-infection with bacteria can also contribute to a severe, rapidly progressive illness. Bacteria frequently reported include Streptococcus pneumoniae and Staphylococcus aureus, including methicillin-resistant strains in some cases. As these bacterial co-infections are more frequent than initially recognized, clinicians stressed the need to consider empiric antimicrobial therapy for community acquired pneumonia as an early treatment.

Groups at greatest risk
Participants agreed that the risk of severe or fatal illness is highest in three groups: pregnant women, especially during the third trimester of pregnancy, children younger than 2 years of age, and people with chronic lung disease, including asthma. Neurological disorders can increase the risk of severe disease in children.

Evidence presented during the meeting further shows that disadvantaged populations, such as minority groups and indigenous populations, are disproportionately affected by severe disease. Although the reasons for this heightened risk are not yet fully understood, theories being explored include the greater frequency of co-morbidities, such as diabetes and asthma, often seen in these groups, and lack of access to care.

Although the exact role of obesity is poorly understood at present, obesity and especially morbid obesity have been present in a large portion of severe and fatal cases. Obesity has not been recognized as a risk factor in either past pandemics or seasonal influenza.

WHO and its partners are providing technical guidance and practical support to help developing countries better detect and treat illness caused by the pandemic virus. Patient care advice that can be applied in resource-limited settings is being rapidly compiled.