Bird flu by the numbers

A farmer walks past baskets of newly hatched ducklings in a hatch room at a poultry egg trading market in Zhejiang province on April 18. (REUTERS)

Late Wednesday afternoon, the New England Journal of Medicine published the first epidemiological report of the H7N9 outbreak in China. To date, the new bird flu strain hassickened 108 people and killed 22; Taiwan has also reported the first case outside of mainland China, a 53-year-old man who recently visited Suzhou and Shanghai (both H7N9 hotspots).

The report covers up to April 17, at which point there were 82 confirmed cases and two suspected cases, and it is chock-full of numbers and statistics. Here are some of the highlights:

63 is the median age of confirmed cases. 73 per cent are male. 86 per cent live in urban areas. 

76 per cent of patients have underlying medical conditions

59 patients -- 77 per cent of the total -- were recently exposed to animals: 76 per cent to chickens, 20 per cent to ducks, seven per cent to swine. Two reported exposures to cats and one to a dog; six said they encountered wild birds and one was exposed to a pet bird.

Four patients worked as poultry workers, three slaughtered poultry at live markets andone transported poultry

Seventeen patients and one suspected case died of acute respiratory distress syndrome or multiorgan failure a median of 11 days after becoming sick.

Among 23 patients where detailed histories could be collected, the median incubation period for the virus was six days.

There have been three family clusters in two provinces, but only detailed information fortwo of them. In the first family, a man visited a live poultry market and observed the slaughter of a chicken which he purchased, cooked and ate two weeks before getting sick; in the second family, a man visited a live poultry market seven days before becoming ill.

Among 81 patients with available data, the median time from the onset of illness to the first medical visit was one day; the median time between getting sick and being hospitalized was 4.5 days.

As of April 17, investigators had detailed information on 678 close contacts of the confirmed patients. 62 per cent were health care workers, 20 per cent were relatives, 18 per cent were social contacts. Respiratory symptoms developed in 19 people who had contact with an H7N9 patient, including 15 health care workers and one medical intern;zero tested positive for H7N9.

The mortality rate for H7N9 is 21 per cent (although the rate will be lower if expanded surveillance efforts find more people who are asymptomatic cases). 

Jennifer Yang is the Star’s global health reporter. She previously worked as a general assignment reporter and won a NNA in 2011 for her explanatory piece on the Chilean mining disaster. Follow her on Twitter: @jyangstar