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.
Need for intensive care
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.
*OBS: Os grifos
do texto são de responsabilidade daquele que está enviando este
documento.
**OBS2: O único óbito
em Campinas em menores de 10 anos foi uma criança com paralisia cerebral
associada a múltiplas malformações do Sistema Nervoso Central.
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