Apr 24, 2013 (CIDRAP News) – Chinese health professionals said in a detailed account today of H7N9 flu cases that about three fourths of patients had underlying medical conditions, and the same percentage had been exposed to animals, including chickens.
Their report, in the New England Journal of Medicine, also included new information about the reported family clusters of cases.
The authors include numerous local- to federal-level health professionals, and their review includes data from 82 cases that were reported as of Apr 17. Since then, the outbreak total has grown to 109 illnesses, including 22 deaths.
The country enhanced its surveillance for the disease after it identified the new virus in March. Among 664 hospitalized patients with unexplained pneumonia, 81 (12.2%) were infected with the new virus. Of 5,551 respiratory specimens from outpatient surveillance for flulike illness, only 1 (0.02%) was positive for H7N9.
Most of the patients who had confirmed infections were men (73%), and most lived in urban settings (84%).
Of 71 patients with available information, 54 (76%) had underlying medical conditions. Among 46 of that group with available data, 40 (87%) were at increased risk due to their age—either younger than 5 years or 65 or older. Four of the patients were poultry workers: Three slaughtered live-market poultry, and one transported poultry.
All but one of the patients was hospitalized. As of the study cut-off date, 17 confirmed case-patients and 1 suspected case-patient had died of acute respiratory distress syndrome or multiorgan failure.
Details about animal exposure were available for 77 of the patients, and 59 (77%) said they had recent exposure to animals while working at or visiting a live-animal market: 45 to chickens, 12 to ducks, and 4 to swine. Other animals included pigeons, geese, quail, wild birds, pet birds, cats, and dogs. A history of animal exposure is unclear for five patients, and investigations are ongoing into their exposures.
The report also sheds new light on the type of contact and exposures that occurred in some of the family clusters, one of which involved some of the first patients who were reported in the outbreak, an 87-year-old man from Shanghai and his two sons.
The report said the index case in the cluster was a 57-year-old brother whose fatal infection was suspected but not confirmed. Within 2 weeks before he got sick, he had visited a live-poultry market where he bought a chicken, observed the slaughtering, brought it home, and cooked it.
After he got sick, his father who lived with him and his 69-year-old brother who lived nearby cared for him, having prolonged unprotected contact before his hospitalization. The father and the brother got sick, and both had lab-confirmed H7N9 infections. The father died from his infection.
The report described another family cluster, a 60-year old man with a suspected infection and his 32-year-old daughter who lived in the same house with other family members.
The father got sick, and his daughter cared for him at home and in the hospital before she got sick. Both of the patients are still critically ill. Tests confirmed H7N9 in the daughter and are still under way on the father. The woman did not raise poultry and had not had any animal exposures.
Today's report also fleshes out more details about contact tracing. Of 1,689 close contacts, excluding the cluster cases, 19 had respiratory symptoms during the 7-day surveillance period. Fifteen were healthcare workers, 1 was a patient in the same ward, 2 were household members, and 1 was a medical intern.
The investigators wrote that the current mortality rate is 21%, but they expect it to increase, given that many of the patients are still critically ill.
So far the H7N9 virus appears more virulent to humans than are other H7 viruses, the group noted.
Though extensive testing is needed to verify the source of H7N9, the Chinese authors strongly suspect poultry that don't show signs of disease. Until the source is confirmed, they said, control measures—such as banning the sale of live birds at markets—could help control the spread of the virus to humans.
Limited human-to-human contact remains a possibility, the scientists wrote, especially in blood relatives. Paired serum samples are being collected from contacts during the case-patients' acute and convalescent illness stages, they added.
They recommend enhanced surveillance to clarify the clinical spectrum of the disease and the extent of asymptomatic infection, along with case-control studies to reveal more about the possible animal and environmental source.
Li Q, Zhou L, Zhou M, et al. Preliminary report: epidemiology of the avian influenza A (H7N9) outbreak in China. N Engl J Med 2013 Apr 24 [Abstract]