*Values are no. (%) except as indicated. ARI, acute respiratory illness; EV, enterovirus; HPIV, human parainfluenza virus; RSV, respiratory syncytial virus. †Occurring when EV-D68 is detected in a secondary household member 1–14 days after index case. ‡Unlikely secondary transmission defined as occurring when only 1 EV-D68 case is detected in the household or when >2 EV-D68 cases are in a household but secondary case detected >14 days after index case. §Underlying conditions include asthma, chronic obstructive pulmonary disease (including chronic bronchitis and emphysema), sleep apnea, heart disease, congenital heart disease, heart failure, Down syndrome, hypertension (high blood pressure), diabetes (high blood sugar), liver condition, weak or failing kidneys, cancer or malignancy, arthritis, stroke, deep vein thrombosis or pulmonary embolism, sickle cell disease or thalassemia, weakened immune system, depression, anxiety, thyroid issues, or other health diagnosis. ¶Rhinovirus target was detected in 32 (91.4%) samples but is not shown because of cross-reactivity between that target and EV-D68 and several other enterovirus species (assay ID Vi99990016_po, Thermo Fisher [https://www.thermofisher.com]). #Symptoms reported <7 days of the individual EV-D68 illness episode’s first positive specimen collection, including fever​, cough​, sore throat​, shortness of breath​, myalgia​, rhinorrhea, or a combination of symptoms. All persons included reported >1 symptom. **Self-reported care seeking defined as seeking healthcare from a healthcare provider during illness. ††Includes masking, sleeping separately, covering cough or sneeze before or during illness episode. ‡‡Includes handwashing, cleaning, disinfecting.