TABLE. Characteristics of reported pediatric influenza-associated encephalopathy cases — United States, 2024–25 influenza season.
| Characteristic | All cases |
ANE |
Other IAE |
|||
|---|---|---|---|---|---|---|
| n/N* | Column % | n/N | Column % | n/N | Column % | |
|
Total (row %)
|
109
|
100
|
37
|
34
|
72
|
66
|
| Median age, yrs (IQR) |
5 (3–10)
|
—
|
4 (1–7) |
— |
6 (4–10) |
— |
|
Age group, yrs
| ||||||
| 0–4 |
44/109
|
40
|
22/37 |
59 |
22/72 |
31 |
| 5–11 |
46/109
|
42
|
11/37 |
30 |
35/72 |
49 |
| 12–17 |
19/109
|
17
|
4/37 |
11 |
15/72 |
21 |
|
Female sex
|
49/107
|
46
|
18/37 |
49 |
31/70 |
44 |
|
Race and ethnicity†
| ||||||
| Asian, non-Hispanic |
7/102
|
7
|
4/35 |
11 |
3/67 |
4 |
| Black or African American, non-Hispanic |
19/102
|
19
|
4/35 |
11 |
15/67 |
22 |
| Hispanic or Latino |
16/102
|
16
|
8/35 |
23 |
8/67 |
12 |
| White, non-Hispanic |
53/102
|
52
|
18/35 |
51 |
35/67 |
52 |
| Other, non-Hispanic |
7/102
|
7
|
1/35 |
3 |
6/67 |
9 |
|
U.S. Census Bureau region§
| ||||||
| Northeast |
31/109
|
28
|
6/37 |
16 |
25/72 |
35 |
| Midwest |
26/109
|
24
|
8/37 |
22 |
18/72 |
25 |
| South |
31/109
|
28
|
14/37 |
38 |
17/72 |
24 |
| West |
21/109
|
19
|
9/37 |
24 |
12/72 |
17 |
|
Hospital admission month¶
| ||||||
| Before influenza peak (Oct–Dec) |
13/109
|
12
|
5/37 |
13 |
8/72 |
11 |
| During influenza peak (Jan–Feb) |
71/109
|
65
|
29/37 |
78 |
42/72 |
58 |
| After influenza peak (Mar–May) |
25/109
|
23
|
3/37 |
8 |
22/72 |
31 |
|
Underlying medical conditions**,††
| ||||||
| None |
58/106
|
55
|
18/35 |
51 |
40/71 |
56 |
| At least one |
48/106
|
45
|
17/35 |
49 |
31/71 |
44 |
| Asthma |
12/106
|
11
|
3/35 |
9 |
9/71 |
13 |
| Seizure disorder |
10/106
|
9
|
5/35 |
14 |
5/71 |
7 |
| Neurologic or neuromuscular disease |
15/106
|
14
|
5/35 |
14 |
10/71 |
14 |
|
Signs and symptoms on admission§§
| ||||||
| Altered mental status¶¶ |
93/106
|
88
|
32/35 |
91 |
61/71 |
86 |
| Fever |
92/108
|
85
|
34/37 |
92 |
58/71 |
82 |
| Headache |
22/86
|
26
|
5/28 |
18 |
17/58 |
29 |
| Respiratory tract symptoms |
91/104
|
87
|
33/36 |
92 |
58/68 |
85 |
| Seizures |
56/94
|
60
|
28/32 |
87 |
28/62 |
45 |
|
Illness onset to neurologic symptom onset days, (IQR)***
|
2 (1–3)
|
—
|
2 (1–3) |
— |
2 (1–4) |
— |
|
Influenza vaccine status
†††
| ||||||
| Received the 2024–25 seasonal influenza vaccine ≥14 days before illness onset |
15/93
|
16
|
4/30 |
13 |
11/63 |
17 |
|
Influenza antiviral treatment
| ||||||
| Received an influenza antiviral§§§ |
86/102
|
84
|
31/33 |
94 |
55/69 |
80 |
| Illness onset to antiviral start date, days (IQR)*** |
3 (1–4)
|
—
|
2 (2–4) |
— |
3 (2–4) |
— |
| Started before admission |
8/80
|
10
|
2/27 |
7 |
6/53 |
11 |
| Started on or after admission |
72/80
|
90
|
25/27 |
93 |
47/63 |
89 |
|
Other treatment
| ||||||
| Immunomodulators*** |
17/80
|
21
|
14/25 |
56 |
3/55 |
5 |
| Intravenous immunoglobulin*** |
23/79
|
29
|
16/24 |
67 |
7/55 |
13 |
| Plasma exchange*** |
15/80
|
19
|
11/25 |
44 |
4/55 |
7 |
| Systemic corticosteroids |
52/98
|
53
|
29/33 |
88 |
23/65 |
35 |
| Vasopressors*** |
25/79
|
32
|
17/24 |
71 |
8/55 |
15 |
|
Influenza virus type or subtype
| ||||||
| Influenza A |
97/109
|
89
|
34/37 |
92 |
63/72 |
87 |
| Influenza A (H1N1) |
37/59
|
63
|
13/23 |
56 |
24/36 |
67 |
| Influenza A (H3N2) |
22/59
|
37
|
10/23 |
43 |
12/36 |
33 |
| Influenza B |
12/109
|
11
|
3/37 |
8 |
9/72 |
12 |
|
Bacterial, viral, or fungal detection¶¶¶
|
13/109
|
12
|
5/37 |
13 |
8/72 |
11 |
|
Neuroimaging performed**** | ||||||
| Yes |
102/108
|
94
|
37/37 |
100 |
65/71 |
92 |
| No |
6/108
|
6
|
0 |
0 |
6/71 |
8 |
| Abnormal findings†††† |
68/102
|
67
|
36/37 |
97 |
32/65 |
49 |
|
Illness severity
| ||||||
| Median length of hospitalization among survivors, days (IQR)§§§§ |
9 (3–24)
|
—
|
30 (18–38) |
— |
6 (3–17) |
— |
| Median length of hospitalization among patients who died, days (IQR)§§§§ |
4 (3–7)
|
—
|
4 (3–7) |
— |
5 (1–8) |
— |
| Pneumonia diagnosis at admission |
19/101
|
19
|
6/34 |
18 |
13/67 |
19 |
| Admitted to an ICU |
80/108
|
74
|
37/37 |
100 |
43/71 |
61 |
| Invasive mechanical ventilation |
59/109
|
54
|
33/37 |
89 |
26/72 |
36 |
| Not at neurologic baseline at discharge¶¶¶¶ |
33/70
|
47
|
12/13 |
92 |
21/57 |
37 |
| Death | 21/109 | 19 | 15/37 | 41 | 6/72 | 8 |
Abbreviations: ANE = acute necrotizing encephalopathy; IAE = influenza-associated encephalopathy; ICU = intensive care unit.
* Denominators are adjusted throughout the table to exclude missing and unknown responses.
† Children with multiple races selected and non-Hispanic ethnicity selected were categorized as “Other, non-Hispanic.”
§ Based on state of residence. Censusregionsanddivisions|U.S.CensusBureau
¶ Peak based on national influenza activity for the 2024–25 influenza season. WeeklyUSInfluenzaSurveillanceReport:KeyUpdatesforWeek35,endingAugust30,2025|FluView|CDC
** Underlying medical conditions include the following categories: developmental (e.g., autism and attention deficit hyperactivity disorder), prematurity for those aged <2 years, immunocompromising conditions, chronic metabolic disease, genetic or inborn errors of metabolism, blood disorders, lung disease, cardiovascular disease, renal disease, gastrointestinal disease, rheumatologic disease, and obesity.
†† Two children had underlying medical conditions that can predispose to encephalopathy in the setting of a systemic stressor such as influenza virus. These conditions include an inborn error of metabolism (one) and a leukodystrophy (one).
§§ Numbers are not mutually exclusive.
¶¶ Altered mental status includes delirium, personality changes, hallucinations, and decreased level of consciousness.
*** Optional survey questions included illness onset date, neurologic symptom onset date, and use of other treatments.
††† Among those aged ≥6 months and thus eligible for influenza vaccination. Admission date was used for five IAE patients for whom the illness onset date was not available.
§§§ Seventy-two patients received oseltamivir alone, one received oseltamivir and baloxavir marboxil, six received oseltamivir and peramivir, six received peramivir alone, and one was missing influenza antiviral type information.
¶¶¶ Co-detections were reported from any time during hospitalization for any of the following specimen sources: blood, urine, respiratory tract, peritoneal fluid, or cerebrospinal fluid.
**** Neuroimaging performed included computed tomography of the head and magnetic resonance imaging of the brain.
†††† Percentage of patients with neuroimaging performed.
§§§§ To discharge (for survivors) or death; data were missing for five IAE patients (two ANE and three other IAE).
¶¶¶¶ Among patients who survived, were no longer hospitalized, and for whom survey data were available.