Differences in the Epidemiology of Childhood Infections with Avian Influenza A H7N9 and H5N1 Viruses

Abstract

The difference between childhood infections with avian influenza viruses A(H5N1) and A(H7N9) remains an unresolved but critically important question. We compared the epidemiological characteristics of 244 H5N1 and 41 H7N9 childhood cases (<15 years old), as well as the childhood cluster cases of the two viruses. Our findings revealed a higher proportion of H5N1 than H7N9 childhood infections (31.1% vs. 6.4%, p = 0.000). However, the two groups did not differ significantly in age (median age: 5.0 vs. 5.5 y, p = 0.0651). The proportion of clustered cases was significantly greater among children infected with H5N1 than among children infected with H7N9 [46.7% (71/152) vs. 23.6% (13/55), p = 0.005], and most of the childhood cases were identified as secondary cases [46.4% (45/97) vs. 33.3% (10/30), p = 0.000]. Mild status accounted for 79.49% and 22.66%, severe status for 17.95% and 2.34%, and fatal cases for 2.56% and 75.00% of the H7N9 and H5N1 childhood infection cases (all p<0.05), respectively. The fatality rates for the total, index and secondary childhood cluster cases were 52.86% (37/70), 88.5% (23/26) and 33.33% (15/45), respectively, in the H5N1 group, whereas no fatal H7N9 childhood cluster cases were identified. In conclusion, lower severity and greater transmission were found in the H7N9 childhood cases than in the H5N1 childhood cases.

Fig 1. Monthly distribution curve for the total confirmed cases and childhood cases of avian influenza A(H7N9) between February 18, 2013, and June 13, 2016.

Notes: Fig 1a: Total cases (N = 655); Fig 1b: Childhood cases (N = 41).

Fig 2. Monthly distribution curve of confirmed avian influenza A(H5N1) cases in the overall global population and in children between 2006 and June 13, 2016.

Notes: Fig 2a: Total cases (N = 440); Fig 2b: Childhood cases (N = 244).

Fig 3. Age distribution for the total and childhood cases of infection with avian influenza H7N9 and H5N1 viruses.

Notes: Fig 3a: H7N9 total cases (n = 575); Fig 3b: H5N1 total cases (n = 423); Fig 3c: H7N9 childhood cases; Fig 3d: H5N1 childhood cases.

Fig 4. Sex distribution of the confirmed total (n = 641) and childhood (n = 41) avian influenza A(H7N9) cases and of the global total (n = 440) and childhood (n = 244) confirmed H5N1 cases.

Notes: Fig 4a: H7N9 total cases; Fig 4b: H7N9 childhood cases; Fig 4c: H5N1 total cases; Fig 4d: H5N1 childhood cases.

Fig 5. Clinical severity of confirmed avian influenza A(H7N9) cases in children (n = 39) and confirmed H5N1 cases in children (n = 128) worldwide.