Patient Characteristics
A diagnosis of influenza infection was made based on the occurrence of influenza-like symptoms with a positive RT-PCR for influenza A or B [15]. In this study, a total of 388 children with influenza A virus infection (A+ group), 169 children with influenza B virus infection (B+ group), 198 children with influenza-like symptoms who were negative for both influenza A and B viruses (A-B- group) and 259 healthy children (H group) who underwent physical examinations at the same time were included. According to age, all children were divided into three groups: the <1-year-old group, the 1- to 6-year-old group and the >6-year-old group. In the <1-year-old group, there were 18 patients in the A+ group (mean age 0.7±0.2), 3 patients in the B+ group (mean age 0.6±0.2), 19 patients in the A-B- group (age 0.7±0.1), and 38 patients in the H group (mean age 0.6±0.2). In the 1- to 6-year-old group, there were 193 patients in the A+ group (mean age 3.6±1.4), 53 patients in the B+ group (mean age 3.9±1.2), 102 patients in the A-B- group (mean age 3.4±1.2), and 118 patients in the H group (mean age 3.6±1.5). In the >6-year-old group, there were 177 patients in the A+ group (mean age 9.4±2.4), 113 patients in the B+ group (mean age 8.8±2.2), 77 patients in the A-B- group (mean age 9.3±2.6), and 105 patients in the H group (mean age 9.6±2.3). There were no statistically significant differences in the age and sex distributions between groups within the three age groups (P>0.05) (Table 1).
Differences in Routine Blood Parameters in the Three Age Groups
The red blood cell count (RBC) and hemoglobin (Hb) level in the A+ group, B+ group, A-B- group and H group were not significantly different in the groups of patients <1 year old, 1-6 years old and >6 years old. In all three age groups, compared with the H group, the A+ group, B+ group, and A-B- group had lower LYM counts, PLT counts, LMRs and LYM*PLT values, and higher NLRs and MPV/PLT values (Figure 1). In the <1-year-old group, there were no significant differences in the LYM count, PLT count, LMR, NLR, LYM*PLT and MPV/PLT between the A+ group and A-B- group. There were only 3 patients in the B+ group, so no statistical analysis was performed. In the 1- to 6-year-old group, the LYM count, PLT count, LMR, LYM*PLT and MPV/PLT were significantly different between the A+ group and the A-B- group and the LYM count, LMR and LYM*PLT were significantly different between the B+ group and the A-B- group (Figure 1). In the >6-year-old group, the LYM count, LMR, NLR and LYM*PLT were significantly different between the A+ group and the A-B- group; the PLT count, LMR and LYM*PLT were significantly different between the B+ group and the A-B- group (Figure 1)
Value of the LYM Count, PLT Count, LMR, NLR, LYM*PLT, and MPV/PLT for the Prediction of Influenza
1- to 6-year-old A+ group
The variable that best predicted positivity for influenza virus A based on the area under the curve (AUC) was the LMR. When the A-B- group was taken as a reference, the cutoff value was 3.75, the AUC was 0.886, and the sensitivity and specificity were 81.87% and 84.31%, respectively. When the H group was used as the reference, the maximum AUC was obtained with the LYM*PLT (followed by the LMR); the cutoff value of the LYM*PLT was 680.48, the AUC was 0.958, and the sensitivity and specificity were 90.67% and 89.66%, respectively (Figure 2).
1- to 6-year-old B+ group
The variable that best predicted positivity for influenza virus B based on the AUC was the LMR. When the A-B- group was taken as a reference, the cutoff value was 3.71, the AUC was 0.843, and the sensitivity and specificity were 73.58% and 84.31%, respectively. When the H group was used as the reference, the cutoff value for the LMR was 4.47, the AUC was 0.918, and the sensitivity and specificity were 86.79% and 89.66%, respectively (Figure 3).
>6-year-old A+ group
The maximum AUC was obtained with the LMR. When the A-B- group was taken as a reference, the cutoff value was 3.05, the AUC was 0.949, and the sensitivity and specificity were 89.27% and 89.61%, respectively. When the H group was a reference, the cutoff value was 3.09, the AUC was 0.975, and the sensitivity and specificity were 90.40% and 95.24%, respectively (Figure 4).
>6-year-old B+ group
The maximum AUC was obtained with the LMR. When the A-B- group was taken as a reference, the cutoff value was 2.88, the AUC was 0.924, and the sensitivity and specificity were 83.19% and 92.21%, respectively. When the H group was a reference, the cutoff value of the LMR was 3.48, the AUC was 0.954, and the sensitivity and specificity were 90.27% and 92.38%, respectively (Figure 5).