Mild infection of a novel H7N9 avian influenza virus in children in Shanghai

Yu, Xuelian; Zhang, Xi; He, Yi; Wu, Huanyu; Gao, Xia; Pan, Qichao; Shen, Jiaren; Zhu, Jianming; Chen, Hongyou; Zhu, Yiyi; Wu, Fan; Wang, Jianwei; Yuan, Zhengan

The clinical course and outcome of disease appears to be more favorable in children than adults when infected with highly pathogenic viruses, such as H5N1, novel H7N9 or severe acute respiratory syndrome coronavirus. Several possible reasons may account for this finding: parents take children to visit doctors when the children become sick or anti-viral drugs are more likely to be prescribed to sick children with a high fever. Another important factor for a severe clinical course of H7N9 infection may relate to impaired host immune function. Similar circumstances have been reported for measles infections. Research in measles found that remarkable lymphopenia occurred in measles cases, with a reduction in the number of T cells, B cells, neutrophils and monocytes. The severity of illness in patients parallels the severity and duration of lymphopenia, 14 which is in turn age dependent, with less severe cases in young children but more severe cases in adults. The novel H7N9 virus may act in a similar manner as measles. More fatal cases (40%, 4/10) showed lower leukocyte counts than severe (14.3%, 1/7) or mild cases (0/0), and fatal cases also showed a higher neutrophil percentile (60%, 6/10) than severe (28.6%, 2/7) or mild cases (0/0). In addition, fatal cases (100%, 3/3) showed lower lymphocyte percentiles than severe (28.6%, 2/7) or mild cases (0/0). The lymphocyte subpopulation measurement of one child patient showed downregulated CD16 1 CD56 1 natural killer cells. Attenuated natural killer functions were observed previously in H5N1 infected patients. 15 Therefore, we propose that the novel H7N9 virus may induce transient immunosuppression that occasionally results in fatal opportunistic infections, especially in patients with underlying diseases. Our data are limited in the present study, and further research addressing host immune functions relating to H7N9 infection with a larger sample size may provide better answers.