To investigate the characteristics of lymphocyte subsets in children with severe influenza A, and to evaluate their diagnostic value for children with severe influenza A.

A retrospective study was conducted on 129 hospitalized children with influenza A within 48 hours in Beijing Ditan Hospital, Capital Medical University from October 2018 to December 2019. A 1∶2 match was made according to age and sex. Only those with fever and upper respiratory symptoms were classified as mild group (43 cases); those with persistent high fever > 3 days, and those with pneumonia, dyspnea and altered consciousness were classified as severe group (86 cases). Blood routine examination and lymphocyte subsets of the two groups were detected and compared. The diagnostic efficacy of each parameter of lymphocyte subsets in severe influenza A were analyzed by receiver operating characteristic curve (ROC), while the area under the curve (AUC) of each parameter were compared in pairs by Medcalc software.

Lymphocyte count [1 554 (928, 2 605) cells/μl vs. 2 723 (1 792, 4 108) cells/μl] and T cell count [728 (419, 1 491) cells/μl vs. 1 558 (1 123, 2 259) cells/μl], CD4⁺ T cell count [418 (237, 699) cells/μl vs. 1 558 (1 123, 2 259) cells/μl] decreased, all with significant differences (Z =-3.959, -2.833, -4.399; P < 0.001, 0.005, < 0.001). The sensitivity and specificity of CD4⁺ T cell count were 60.4% and 95.5%, the area under the curve (AUC) was 0.825 (95%CI: 0.715-0.905). The AUC of CD4⁺ T cell count compared with that of CD8⁺ T cell count, NK cell count and B cell count were all with significantly difference (Z = 1.961, 2.227, 2.602; P = 0.0498, 0.026, 0.0093), but without significantly difference compared with lymphocyte count and T cell count (Z = 1.016, 1.372; P = 0.310, 0.17).

The cellular immune function of children with severe influenza A is impaired at early stage of the disease. CD4⁺ T cell count within 48 hours of the disease has good diagnostic efficacy for severe influenza A.