Influenza


In a Canadian review of 324 hospitalized children, 51% of infected children had an underlying disease and the majority of these children were ≥2 years of age. However, a general increase in the proportion of admissions was observed in children over two years of age. The clinical presentation was fever and cough in 90%, 67% had wheezing, pneumonia, or respiratory distress and secondary bacterial infections were rare (3.4%). Half of the children presented with gastrointestinal involvement. The ICU admittance rate was 17% and the hospitalized fatality rate was <2%.45


In Argentina, similar characteristics to those listed above were reported in 251 hospitalized children. Interestingly, viral co-infection occurred in 19%, of whom 75% were under two years of age, and in almost all cases the virus was respiratory syncytial virus (RSV).46


The OR


for admission to the ICU in patients with asthma was 4.92; meanwhile, oncological patients undergoing chemotherapy and those with HIV had a lower risk for ICU admittance. There was no survival benefit with corticosteroid use in the ICU. The mortality rate was 10 times higher than that seen with previous seasonal influenza and five-times higher than the rate in the US, as reported by the Centers for Disease Control and Prevention (CDC). When analysing the infant mortality subgroup, a 10-fold higher rate was seen compared with the US. Two-thirds died of refractory hypoxemia and had comorbidities associated with an increased risk for death.


Pregnant women with confirmed influenza represented 7–10% of hospitalized patients, 6–9% of ICU patients, and 6–17.6% of patients who died (mainly immunosuppressed women and women in the last trimester of pregnancy), with a six-fold higher mortality rate compared with immunocompetent women.11,17,22,36


Ninety-five percent of infected women


were in the second or third trimester of pregnancy. Women who were pregnant presented with a four-fold higher rate of hospital admissions than the general population. Twenty-five percent of post-partum women and 60% of pregnant women had comorbidities known to increase the risk for complicated influenza, of which asthma was the most frequent (16 versus 28% in non-pregnant women). However, 36% of those requiring intensive care were previously healthy, usually presenting with mild or moderate disease and rapid progression and worsening.


Nineteen percent of pregnant and 50% of post-partum women required intensive care, of whom 73% required mechanical ventilation and 15% underwent ECMO.47


antiviral agents. Immunocompromized patients accounted for 20% of hospitalized patients, the majority of whom were receiving corticosteroid treatment. Although there was a low incidence of influenza among hematopoietic stem cell transplant recipients, these patients had a 28% mortality rate if they developed pneumonia. Influenza causes significant morbidity among solid-organ transplant recipients; there was a higher incidence of influenza among those who had undergone lung transplantation, probably secondary to transplantation-related impaired mechanisms of viral clearance. The mortality rate among leukemia patients undergoing chemotherapy was 25%.22


HIV-infected patients with severe H1N1v infection were uncommon. Limited data from South Africa report a mortality rate of 0.4%, although HIV-infected patients often presented with a prolonged duration of illness. Other studies also show that patients under effective antiretroviral therapy had decreased hospitalization and mortality rates.48


Diagnostic Features


Nasopharyngeal aspirate was found to contain the highest amount of viral loads by a significant degree, and thus is the ideal specimen. However, other airway secretions can be used. In intubated patients, endotracheal aspirates and bronchoalveolar lavage are suitable.49,50


19% of patients with viral pneumonia tested negative in upper respiratory tract samples and positive in lower respiratory tract samples. Moreover, an initial false-negative rate of 10% in lower airway samples has been reported. Thirty-eight percent of false-negative results with rapid antigen testing were seen in pregnant women.17 Therefore, clinical decisions cannot be made on the basis of negative results. In patients with ILI, the positive predictive value of rapid antigen testing increases by 50%.50


Rapid antigen testing has a low sensitivity (17.8–53%) for influenza A H1N1v:10


Viral cultures are highly sensitive and 100%


specific, but do not differentiate between influenza A strains and take two to seven days to yield results. Reverse-transcriptase polymerase chain reaction (rt-PCR) testing is the current gold standard, with 500-fold higher sensitivity compared with cultures. Multiplex rt-PCR yields influenza A subtypes with concurrent detection of a wide range of respiratory viruses. Quantitative assays are less sensitive but are useful for monitoring purposes. A false-negative rate of up to 19% with rt-PCR has been described in specimens from the upper and lower respiratory tract;50


thus, when there is high clinical suspicion, new specimens


Bacterial pulmonary co-infection was described, but was rare. Most maternal deaths were related to the initiation of antiviral therapy 48 hours or more after the onset of symptoms, and 75% had underlying medical conditions. Fetal morbidity (increased congenital abnormalities) and mortality was high secondary to the indirect effects of influenza infection such as maternal fever and severe hypoxemia. Premature births occurred in almost all deliveries owing to either spontaneous vaginal delivery or urgent Caesarean. Complications in these infants were related exclusively to prematurity and there were no reported deaths. Even though the influenza virus crosses the placenta, viremia is infrequent and none of the infants in this group was diagnosed with influenza.


Immunocompromized patients were at risk for severe disease owing to prolonged viral shedding and increased risk for resistance to


68


should be collected. Treatment


Neuraminidase inhibitors (NIs) such as oseltamivir, zanamivir, and peramivir are effective against H1N1v, while M2 inhibitors such as amantadine and rimantadine have no activity against it.7,8


Oseltamivir is


the drug of choice, administered orally or by nasogastric tube (in critically ill patients). Maximum doses of 450mg twice daily have been administered without significant adverse event rates.8


Dose


Zanamivir (endovenous) is used in patients with oseltamivir viral resistance (OVR) or when the oral route is not available.52 administration is effective, with only 10–20% absorption,20


related to mild bronchospasm. Peramivir, which is widely available in US RESPIRATORY DISEASE


adjustment is recommended in patients with renal dysfunction and renal replacement. Neuropsychiatric adverse events have been reported.21,51


Inhaled but has been


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