Swine flu ’killing 11% of infected patients’

Swine flu is killing more than a tenth of those it infects in California and up to 20% of older victims, a study has shown.

Researchers in the US state also found almost a third of cases required intensive care treatment. Hospital admissions and death could occur “at all ages”.

The findings, published in the Journal of the American Medical Association (Jama), fly in the face of common perceptions of swine flu being a generally mild illness.

The US researchers looked at 1,088 cases of swine flu reported in California between April 23 and August 11 this year.

Of these, 32% were children under the age of 18, with infants having the highest rates of hospital admissions. The midpoint age of patients was 27.

In total, 340 patients (31%) were admitted to hospital intensive care units. Of the 297 intensive care cases for whom information was available, 65% required mechanical ventilation.

Chest X-rays of 833 patients revealed indications of pneumonia or acute respiratory distress syndrome.

The researchers recorded 118 deaths. Fatalities were most common among people aged 50 and over, who had a mortality rate of between 18% and 20%. Seven per cent of deaths were among children younger than 18.

Among fatal cases, it typically took just 12 days after the onset of symptoms for the patient to die. The most common causes of death were viral pneumonia and acute respiratory distress syndrome.

The authors, led by Dr Janice Louie from the California Department of Public Health, wrote: “In contrast with the common perception that pandemic 2009 influenza A (H1N1) infection causes only mild disease, hospitalisation and death occurred at all ages, and up to 30% of hospitalised cases were severely ill.”

Most patients admitted to hospital had underlying health problems, including high blood pressure and obesity, said the scientists. They suggested obesity might be a newly identified risk factor for fatal swine flu infection.

The researchers added: “Clinicians should maintain a high level of suspicion for pandemic 2009 influenza A (H1N1) infection in patients presenting currently with influenza-like illness who are older than 50 years or have known risk factors for influenza complications, regardless of rapid test results. Hospitalised infected cases should be carefully monitored and treated promptly with anti-viral agents.”

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