Zoonotic Transmission of Avian Influenza Virus (H5N1), Egypt, 2006–2009

A lower case-fatality rate may have been caused by a less virulent virus clade.

D uring January 2003-March 2009, a total of 417 human cases of avian infl uenza (H5N1) and 256 deaths (61%) were reported worldwide (1). Although human-tohuman transmission has occurred (2)(3)(4), most human cases have been caused by zoonotic transmission from poultry (5)(6)(7)(8). Investigations have emphasized the need for timely identifi cation to determine demographic groups at risk and activities more likely to cause human infection so that control and prevention measures may be implemented. Such investigations may also determine whether the virus can cause pandemic disease. , a total of 3,941 asymptomatic persons exposed to avian infl uenza (H5N1) from a person with a confi rmed case or from infected poultry were tested by using a real-time PCR; none were positive.
In March 2006, the fi rst human case of avian infl uenza (H5N1) in Egypt was reported from Qalubiya Governorate ( Figure 1). We report the fi rst 63 human cases. We also describe affected demographic groups, illness, mortality rates, and specifi c events that contributed to transmission.

Materials and Methods
The study protocol (NAMRU3. 2004 The number of patients for whom data were available is noted. Children are defi ned as persons <15 years of age, adults as persons >15 years of age, delayed hospitalization as >2 days between illness onset and hospitalization, and delayed oseltamivir as >2 days between illness onset and the fi rst oseltamivir dose. Univariate analyses were performed by using Epi Info version 3.4.1 (Centers for Disease Control and Prevention, Atlanta, GA, USA). Unless otherwise noted, χ 2 or Fisher exact tests were used. Multivariate analysis to identify risk factors for death was performed by using a backward, stepwise logistic regression model starting with all variables (dichotomized at their median value) signifi cant by univariate analyses. The Wald statistic and log-likelihood ratio were used to exclude variables. Multivariate analyses were performed by using SPSS version 18 (SPSS Inc., Chicago, IL, USA).

Overview
During March 2006-March 2009, a total of 6,355 suspected cases of avian infl uenza (H5N1) were reported, and samples were tested by the Central Public Health Laboratory. Of these, 63 (1%) cases were confi rmed and 24 were fatal (case-fatality rate 38%) ( Table 1). Among 63 casepatients, median age was 10 years (range 16 months-75 years), 24 (38%) were women >15 years of age, 5 (8%) were men >15 years of age, 16 (25%) were girls <15 years of age, and 18 (29%) were boys <15 years of age (Table 1). Two infected women were pregnant; both died of respiratory failure. Clinical or exposure data were not available for 2 case-patients (a 31-year-old man infected in Egypt who became ill and whose infl uenza was diagnosed in Jordan, and a 75-year-old woman who died within hours of hospitalization). Risk factor data on exposure to birds were available for 41 case-patients (Table 1)  clusters, all shared a common exposure to likely infected poultry and became ill at the same time. In the third cluster, although illness onsets were separated by 4 days, an investigation showed that each child had 2 separate exposures to infected birds. Human-to-human infections were not identifi ed. Household contacts were not given oseltamivir but were followed up closely for 10 days. Secondary infections were not found.
Of 19 case-patients with acute respiratory distress syndrome, 18 died. The only survivor was an 18-year-old woman who received intubation for 12 days and oseltamivir 2 days after illness onset. A complication was more likely to develop in adults; 20 (77%) of 26 had >1 complication compared with only 5 (15%) of 33 children (p<0.001).

Oseltamivir Treatment, Virus Isolates, and Oseltamivir Resistance
All 62 case-patients who became ill in Egypt received >1 dose of oseltamivir. Of 58 patients for whom complete data for oseltamivir was available, 25 (43%) received their fi rst dose <48 hours after illness onset; all but 1 survived. Median duration of treatment was 8 days (range 1-37 days). The fi rst dose of oseltamivir was more likely to be delayed for adults. Twenty (80%) of 25 adults had a delay before receiving oseltamivir compared with 13 (39%) of 33 children (p = 0.005).
Virus isolates were obtained from 34 (54%) of 63 case-patients. Sequencing of hemagglutinin and neuraminidase genes showed all viruses belonged to clade 2.2 and were closely related to isolates from birds in Europe and the Middle East (10). Drug sensitivity was determined for all isolates. Resistance to oseltamivir was confi rmed in viruses from 2 patients in the same family; both died. Resistance was observed in the initial diagnostic sample and did not occur during treatment. A mutation at position N294S conferring a 12-15× reduction in drug susceptibility was identifi ed in both isolates (11).
Although adults were more likely than children to have a delay in hospitalization, age >15 years and delayed hospitalization were independently associated with higher mortality rates. Of 28 adults for whom hospitalization data were available, 12 (43%) were hospitalized in the fi rst 48 hours of illness compared with 27 (79%) of 34 children (p = 0.007). Stratifi ed analysis showed delayed hospitalization was a greater risk factor for death among adults than among children. Eighteen (86%) of 20 adults hospitalized >48 hours after illness onset died compared with 4 (50%) of 8 adults hospitalized <48 hours after illness onset (p = 0.04). None of 24 children hospitalized <48 hours after illness onset died compared with 2 (20%) of 10 children hospitalized >48 hours after illness onset. Nineteen (83%) of 23 female patients hospitalized >48 hours after illness onset died compared with 2 (12%) of 17 hospitalized <48 hours after illness onset (p<0.001).
Eighteen (90%) of 20 adults whose fi rst oseltamivir dose was delayed died compared with 1 (20%) of 5 adults whose fi rst oseltamivir dose was not delayed (p = 0.005). None of 20 children who received oseltamivir <48 hours of illness onset died compared with 1 (8%) of 13 children whose fi rst dose was delayed.
Age, sex, delayed hospitalization, and delayed use of oseltamivir were included in multivariate analysis by using a logistic model to identify risk factors for death. Sex and delayed hospitalization did not contribute to the fi nal model. Because of relatively few cases, high degree of covariance in age, and delayed use of oseltamivir, there was insuffi cient power to further develop this model. Despite this limitation, analysis showed that age >15 years and having received a fi rst dose of oseltamivir >2 days after illness onset were likely independent risk factors contributing to death.

Exposure
Handling live domestic poultry likely infected with avian infl uenza virus (H5N1) was the primary source of exposure. Investigations showed that human-to-human transmission was unlikely; even clusters of case-patients had exposure to infected poultry. Of 63 case-patients, 4 (6%) were involved in poultry production or distribution (3 poultry farm workers and 1 seller), 2 (3%) had unknown poultry exposure, and 57 had direct contact with backyard poultry (Table 1).
Exposure data were available for 41 of 57 case-patients with exposure to backyard fl ocks. Of these case-patients, 33 (80%) reported having had ill birds in their egg-laying fl ocks and 12 (29%) had recently bought poultry. Of these 12 case-patients, 7 (58%) reported that purchased birds became ill after being brought home. Of 27 case-patients for whom information was documented, 13 (48%) slaughtered or defeathered birds (Table 1). No case-patients reported eating raw or undercooked animal products.

Discussion
In February 2006, avian infl uenza (H5N1) emerged among domestic poultry in the Nile Delta of Egypt. Within 4-5 weeks, it had affected commercial farms and backyard fl ocks throughout Egypt and resulted in zoonotic transmission to 10 persons in many governorates. Currently, Egypt has reported the third largest number of cases of avian infl uenza (H5N1) after Indonesia and Vietnam (1).
The mortality rate for avian infl uenza (H5N1) in Egypt (38%) is lower than that in other countries. As of March 2009, mortality rates were 82% in Indonesia, 50% in Vietnam, 66% in the People's Republic of China, and 68% in Thailand. Explanations for this observation include lower mortality rates for certain demographic groups, clinician awareness resulting in improved medical care, or less pathogenic virus. The most striking fi nding is the low mortality rate for children. Although children represent 54% of reported infections, they account for only 8% of deaths. This high survival rate is unlikely to be caused by young age alone. Children were hospitalized earlier in the clinical course of their illness, were more likely to receive oseltamivir within the fi rst 2 days, and appeared to be less ill than adults, as noted by the high proportion of chest radiographs with no abnormal fi ndings and the low proportion of children with respiratory failure. Differences in sensitivity of surveillance methods among countries must also be considered.
One must also consider whether the 2.2 virus clade is less virulent. This suggestion is not supported by a report of the 2005-2006 outbreak of clade 2.2 virus (H5N1) in Turkey, where of 8 patients 5-15 years of age, 4 (50%) died (6).
Despite overall low mortality rates, particularly among children, the mortality rate in women was >52%. This rate could be due to reasons that include receiving a higher  virus inoculum to the lungs through activities associated with slaughtering and defeathering birds, a more profound proinfl ammatory cytokine response, or delay in receiving healthcare. Only delay in receiving healthcare was examined in this study. Women reported a longer time between illness onset and hospitalization and a longer time until the fi rst dose of oseltamivir than men. Women and men who sought healthcare were admitted to the same facilities and received identical care.
More than 5,000 asymptomatic persons known to have been exposed to poultry infected with avian infl uenza virus (H5N1) or in contact with confi rmed human case-patients were followed up clinically and tested by using real-time PCR. Although prophylaxis was not given, infl uenza-like illnesses were not observed and all persons showed negative results. Although serologic testing is needed to exclude infection with avian infl uenza virus (H5N1), it was unlikely that a large proportion of these persons with high-level exposures to infected birds or humans became infected and supports the decision of the MOH to discontinue testing asymptomatic persons. This fi nding is consistent with those of studies in Thailand (12) and Cambodia (13).
Although infection and illness do not develop in most persons exposed to infected poultry, all but 2 cases were attributed directly to exposure to poultry likely infected with avian infl uenza virus (H5N1). No illnesses were attributed to exposure to wild birds. Although 3 family clusters were identifi ed, all 7 persons in these clusters had independent exposures. Many families in Egypt raise backyard fl ocks for eggs and purchase live poultry for meat. Among casepatients, the likely route of infection appears to be direct handling, slaughtering, or defeathering infected birds recently purchased for meat and mingling of recently purchased birds with egg-laying fl ocks. Recently purchased birds were frequently slaughtered before illness was noted, and purchase was often followed by illness and death among egg-producing fl ocks.
Contact between backyard fl ocks and wild infected birds could not be estimated, but exposure to feral poultry in canals and waterways near affected households was common. Because persons in Egypt rely on live poultry purchased at markets for dietary protein, the price of poultry infl uences poultry-buying practices of families. Women in several affected families noted exceptionally low prices for healthy looking birds. These prices indicated that they might be buying infected birds. This fi nding was true when prices of beef increased in response to decreased availability or increased demand. Despite this knowledge, most persons believed they would be able to slaughter and prepare birds before they became ill or died. This belief was true in most cases but recently purchased birds frequently infected egg-laying fl ocks, which died within days of exposure.
Despite knowledge of overall exposure patterns and identifi cation of groups at risk for exposure, little detailed information on activities that result in infection is available. Although slaughtering and defeathering infected birds appear to be high-risk practices, there have likely been thousands of infected birds sold and slaughtered in homes in Egypt over the past 3 years. Despite this suggestion, we have reports of only 63 cases. Although exposure to avian infl uenza virus (H5N1) infection is necessary for infection, exposure is not suffi cient to explain the epidemiology of cases of avian infl uenza (H5N1) in Egypt. Whether there is another unknown risk factor or variation in the way women slaughter poultry in Egypt is unclear.
Demographics of infl uenza cases in Egypt are different from those in other highly affected countries and are useful for determining exposures and activities that result in infection. Women appear to be at greater risk than men of becoming infected, and, once ill, at greater risk of death. In Egypt, the male:female ratio among patients is 1:1.7 and differs markedly from the 1:1 ratio seen globally (14,15). Caring for or slaughtering poultry is generally the responsibility of women and may explain a higher exposure rate for women. Similarly, age distribution of case-patients differs. In Egypt, 54% of case-patients were <15 years of age, compared with <35% in Indonesia, Vietnam, and China. In Egypt, small children follow their mothers during routine chores, such as feeding and slaughtering poultry. At other times, children will play with poultry, which roam freely around the home. There is a general belief that parents in Egypt will quickly seek medical care for their ill children. This belief is strongly suggested by the fact that children with fever and exposure to dead or ill poultry were consistently evaluated and hospitalized sooner than adults. In addition, many children had mild illness. Mild clinical illness may be caused by early hospitalization, early doses of oseltamivir, or a low virus inoculum.
This report describes 63 human cases of avian infl uenza (H5N1) in Egypt during March 2006-March 2009. During April-July 2009, a total of 20 additional cases were identifi ed (83 cases by the end of July 2009) for which data were not available. Analysis of limited information reported to the World Health Organization showed a median age of 4 years (compared with 10 years for the 63 cases), a case-fatality rate of 15% (compared with 38%), and faster hospitalization after illness onset. Ongoing transmission in the summer of 2009 is indicative of persistent disease in poultry, and limited analysis refl ects the high proportion of infl uenza in children. Thus, avian infl uenza virus (H5N1) remains endemic throughout Egypt. However, human infections are rare and disproportionately affect women and their children, who are responsible for caring for and slaughtering birds within the home. To reduce their risk, specifi c slaughtering practices and other transmission risk factors should be identifi ed and appropriate interventions implemented. In addition, emphasis on controlling domestic poultry populations and increased use of bird cages, hand washing, and other protective measures specifi c for women and children should continue.