Protection From COVID-19 mRNA Vaccination and Prior SARS-CoV-2 Infection Against COVID-19-Associated Encounters in Adults During Delta and Omicron Predominance.

BACKGROUND: Data assessing protection conferred from COVID-19 mRNA vaccination and/or prior SARS-CoV-2 infection during Delta and Omicron predominance periods in the United States are limited. METHODS: This cohort study included persons ≥18 years who had ≥1 health care encounter across 4 health systems and had been tested for SARS-CoV-2 before 26 August 2021. COVID-19 mRNA vaccination and prior SARS-CoV-2 infection defined the exposure. Cox regression estimated hazard ratios (HRs) for the Delta and Omicron periods; protection was calculated as (1-HR)×100%. RESULTS: Compared to unvaccinated and previously uninfected persons, during Delta predominance, protection against COVID-19-associated hospitalizations was high for those 2- or 3-dose vaccinated and previously infected, 3-dose vaccinated alone, and prior infection alone (range, 91%-97%, with overlapping 95% confidence intervals [CIs]); during Omicron predominance, estimates were lower (range, 77%-90%). Protection against COVID-19-associated emergency department/urgent care (ED/UC) encounters during Delta predominance was high for those exposure groups (range, 86%-93%); during Omicron predominance, protection remained high for those 3-dose vaccinated with or without a prior infection (76%; 95% CI = 67%-83% and 71%; 95% CI = 67%-73%, respectively). CONCLUSIONS: COVID-19 mRNA vaccination and/or prior SARS-CoV-2 infection provided protection against COVID-19-associated hospitalizations and ED/UC encounters regardless of variant. Staying up-to-date with COVID-19 vaccination still provides protection against severe COVID-19 disease, regardless of prior infection.

Circulation of Rhinoviruses and/or Enteroviruses in Pediatric Patients With Acute Respiratory Illness Before and During the COVID-19 Pandemic in the US.

Importance: Rhinoviruses and/or enteroviruses, which continued to circulate during the COVID-19 pandemic, are commonly detected in pediatric patients with acute respiratory illness (ARI). Yet detailed characterization of rhinovirus and/or enterovirus detection over time is limited, especially by age group and health care setting. Objective: To quantify and characterize rhinovirus and/or enterovirus detection before and during the COVID-19 pandemic among children and adolescents seeking medical care for ARI at emergency departments (EDs) or hospitals. Design, Setting, and Participants: This cross-sectional study used data from the New Vaccine Surveillance Network (NVSN), a multicenter, active, prospective surveillance platform, for pediatric patients who sought medical care for fever and/or respiratory symptoms at 7 EDs or hospitals within NVSN across the US between December 2016 and February 2021. Persons younger than 18 years were enrolled in NVSN, and respiratory specimens were collected and tested for multiple viruses. Main Outcomes and Measures: Proportion of patients in whom rhinovirus and/or enterovirus, or another virus, was detected by calendar month and by prepandemic (December 1, 2016, to March 11, 2020) or pandemic (March 12, 2020, to February 28, 2021) periods. Month-specific adjusted odds ratios (aORs) for rhinovirus and/or enterovirus-positive test results (among all tested) by setting (ED or inpatient) and age group (<2, 2-4, or 5-17 years) were calculated, comparing each month during the pandemic to equivalent months of previous years. Results: Of the 38 198 children and adolescents who were enrolled and tested, 11 303 (29.6%; mean [SD] age, 2.8 [3.7] years; 6733 boys [59.6%]) had rhinovirus and/or enterovirus-positive test results. In prepandemic and pandemic periods, rhinoviruses and/or enteroviruses were detected in 29.4% (9795 of 33 317) and 30.9% (1508 of 4881) of all patients who were enrolled and tested and in 42.2% (9795 of 23 236) and 73.0% (1508 of 2066) of those with test positivity for any virus, respectively. Rhinoviruses and/or enteroviruses were the most frequently detected viruses in both periods and all age groups in the ED and inpatient setting. From April to September 2020 (pandemic period), rhinoviruses and/or enteroviruses were detectable at similar or lower odds than in prepandemic years, with aORs ranging from 0.08 (95% CI, 0.04-0.19) to 0.76 (95% CI, 0.55-1.05) in the ED and 0.04 (95% CI, 0.01-0.11) to 0.71 (95% CI, 0.47-1.07) in the inpatient setting. However, unlike some other viruses, rhinoviruses and/or enteroviruses soon returned to prepandemic levels and from October 2020 to February 2021 were detected at similar or higher odds than in prepandemic months in both settings, with aORs ranging from 1.47 (95% CI, 1.12-1.93) to 3.01 (95% CI, 2.30-3.94) in the ED and 1.36 (95% CI, 1.03-1.79) to 2.44 (95% CI, 1.78-3.34) in the inpatient setting, and in all age groups. Compared with prepandemic years, during the pandemic, rhinoviruses and/or enteroviruses were detected in patients who were slightly older, although most (74.5% [1124 of 1508]) were younger than 5 years. Conclusions and Relevance: Results of this study show that rhinoviruses and/or enteroviruses persisted and were the most common respiratory virus group detected across all pediatric age groups and in both ED and inpatient settings. Rhinoviruses and/or enteroviruses remain a leading factor in ARI health care burden, and active ARI surveillance in children and adolescents remains critical for defining the health care burden of respiratory viruses.

Association of Culturable-Virus Detection and Household Transmission of SARS-CoV-2, California and Tennessee, 2020-2022.

From 2 severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) household transmission studies (enrolling April 2020 to January 2022) with rapid enrollment and specimen collection for 14 days, 61% (43/70) of primary cases had culturable virus detected ≥6 days post-onset. Risk of secondary infection among household contacts tended to be greater when primary cases had culturable virus detected after onset. Regardless of duration of culturable virus, most secondary infections (70%, 28/40) had serial intervals <6 days, suggesting early transmission. These data examine viral culture as a proxy for infectiousness, reaffirm the need for rapid control measures after infection, and highlight the potential for prolonged infectiousness (≥6 days) in many individuals.

Risk Factors for Reinfection with SARS-CoV-2 Omicron Variant among Previously Infected Frontline Workers.

In a cohort of essential workers in the United States previously infected with SARS-CoV-2, risk factors for reinfection included being unvaccinated, infrequent mask use, time since first infection, and being non-Hispanic Black. Protecting workers from reinfection requires a multipronged approach including up-to-date vaccination, mask use as recommended, and reduction in underlying health disparities.

Increase in Acute Respiratory Illnesses Among Children and Adolescents Associated with Rhinoviruses and Enteroviruses, Including Enterovirus D68 - United States, July-September 2022.

Increases in severe respiratory illness and acute flaccid myelitis (AFM) among children and adolescents resulting from enterovirus D68 (EV-D68) infections occurred biennially in the United States during 2014, 2016, and 2018, primarily in late summer and fall. Although EV-D68 annual trends are not fully understood, EV-D68 levels were lower than expected in 2020, potentially because of implementation of COVID-19 mitigation measures (e.g., wearing face masks, enhanced hand hygiene, and physical distancing) (1). In August 2022, clinicians in several geographic areas notified CDC of an increase in hospitalizations of pediatric patients with severe respiratory illness and positive rhinovirus/enterovirus (RV/EV) test results.* Surveillance data were analyzed from multiple national data sources to characterize reported trends in acute respiratory illness (ARI), asthma/reactive airway disease (RAD) exacerbations, and the percentage of positive RV/EV and EV-D68 test results during 2022 compared with previous years. These data demonstrated an increase in emergency department (ED) visits by children and adolescents with ARI and asthma/RAD in late summer 2022. The percentage of positive RV/EV test results in national laboratory-based surveillance and the percentage of positive EV-D68 test results in pediatric sentinel surveillance also increased during this time. Previous increases in EV-D68 respiratory illness have led to substantial resource demands in some hospitals and have also coincided with increases in cases of AFM (2), a rare but serious neurologic disease affecting the spinal cord. Therefore, clinicians should consider AFM in patients with acute flaccid limb weakness, especially after respiratory illness or fever, and ensure prompt hospitalization and referral to specialty care for such cases. Clinicians should also test for poliovirus infection in patients suspected of having AFM because of the clinical similarity to acute flaccid paralysis caused by poliovirus. Ongoing surveillance for EV-D68 is critical to ensuring preparedness for possible future increases in ARI and AFM.

Magnitude and Determinants of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Household Transmission: A Longitudinal Cohort Study.

BACKGROUND: Households have emerged as important venues for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) transmission. Little is known, however, regarding the magnitude and determinants of household transmission in increasingly vaccinated populations. METHODS: From September 2020 to January 2022, symptomatic nonhospitalized individuals with SARS-CoV-2 infection by RNA detection were identified within 5 days of symptom onset; all individuals resided with at least 1 other SARS-CoV-2-uninfected household member. These infected persons (cases) and their household members (contacts) were subsequently followed with questionnaire-based measurement and serial nasal specimen collection. The primary outcome was SARS-CoV-2 infection among contacts. RESULTS: We evaluated 42 cases and their 74 household contacts. Among the contacts, 32 (43%) became infected, of whom 5 (16%) were asymptomatic; 81% of transmissions occurred by 5 days after the case's symptom onset. From 21 unvaccinated cases, 14-day cumulative incidence of SARS-CoV-2 infection among contacts was 18/40 (45% [95% confidence interval {CI}, 29%-62%]), most of whom were unvaccinated. From 21 vaccinated cases, 14-day cumulative incidence of SARS-CoV-2 infection was 14/34 (41% [95% CI, 25%-59%]) among all contacts and 12/29 (41% [95% CI, 24%-61%]) among vaccinated contacts. At least 1 comorbid condition among cases and 10 or more days of RNA detection in cases were associated with increased risk of infection among contacts. CONCLUSIONS: Among households including individuals with symptomatic SARS-CoV-2 infection, both vaccinated-to-vaccinated and unvaccinated-to-unvaccinated transmission of SARS-CoV-2 to household contacts was common. Because vaccination alone did not notably reduce risk of infection, household contacts will need to employ additional interventions to avoid infection.

Detection of Higher Cycle Threshold Values in Culturable SARS-CoV-2 Omicron BA.1 Sublineage Compared with Pre-Omicron Variant Specimens - San Francisco Bay Area, California, July 2021-March 2022.

Before emergence in late 2021 of the highly transmissible B.1.1.529 (Omicron) variant of SARS-CoV-2, the virus that causes COVID-19 (1,2), several studies demonstrated that SARS-CoV-2 was unlikely to be cultured from specimens with high cycle threshold (Ct) values§ from real-time reverse transcription-polymerase chain reaction (RT-PCR) tests (suggesting low viral RNA levels) (3). Although CDC and others do not recommend attempting to correlate Ct values with the amount of infectious virus in the original specimen (4,5), low Ct values are sometimes used as surrogate markers for infectiousness in clinical, public health, or research settings without access to virus culture (5). However, the consistency in reliability of this practice across SARS-CoV-2 variants remains uncertain because Omicron-specific data on infectious virus shedding, including its relationship with RNA levels, are limited. In the current analysis, nasal specimens collected from an ongoing longitudinal cohort¶ (6,7) of nonhospitalized participants with positive SARS-CoV-2 test results living in the San Francisco Bay Area** were used to generate Ct values and assess for the presence of culturable SARS-CoV-2 virus; findings were compared between specimens from participants infected with pre-Omicron variants and those infected with the Omicron BA.1 sublineage. Among specimens with culturable virus detected, Ct values were higher (suggesting lower RNA levels) during Omicron BA.1 infections than during pre-Omicron infections, suggesting variant-specific differences in viral dynamics. Supporting CDC guidance, these data show that Ct values likely do not provide a consistent proxy for infectiousness across SARS-CoV-2 variants.

Infectious viral shedding of SARS-CoV-2 Delta following vaccination: A longitudinal cohort study.

The impact of vaccination on SARS-CoV-2 infectiousness is not well understood. We compared longitudinal viral shedding dynamics in unvaccinated and fully vaccinated adults. SARS-CoV-2-infected adults were enrolled within 5 days of symptom onset and nasal specimens were self-collected daily for two weeks and intermittently for an additional two weeks. SARS-CoV-2 RNA load and infectious virus were analyzed relative to symptom onset stratified by vaccination status. We tested 1080 nasal specimens from 52 unvaccinated adults enrolled in the pre-Delta period and 32 fully vaccinated adults with predominantly Delta infections. While we observed no differences by vaccination status in maximum RNA levels, maximum infectious titers and the median duration of viral RNA shedding, the rate of decay from the maximum RNA load was faster among vaccinated; maximum infectious titers and maximum RNA levels were highly correlated. Furthermore, amongst participants with infectious virus, median duration of infectious virus detection was reduced from 7.5 days (IQR: 6.0-9.0) in unvaccinated participants to 6 days (IQR: 5.0-8.0) in those vaccinated (P = 0.02). Accordingly, the odds of shedding infectious virus from days 6 to 12 post-onset were lower among vaccinated participants than unvaccinated participants (OR 0.42 95% CI 0.19-0.89). These results indicate that vaccination had reduced the probability of shedding infectious virus after 5 days from symptom onset.

Twelve-Month Follow-up of Early COVID-19 Cases in the United States: Cellular and Humoral Immune Longevity.

We quantify antibody and memory B-cell responses to severe acute respiratory syndrome coronavirus 2 at 6 and 12 months postinfection among 7 unvaccinated US coronavirus disease 2019 cases. All had detectable S-specific memory B cells and immunoglobulin G at both time points, with geometric mean titers of 117.2 BAU/mL and 84.0 BAU/mL at 6 and 12 months, respectively.

Enterovirus D68-Associated Acute Respiratory Illness ─ New Vaccine Surveillance Network, United States, July-November 2018-2020.

Enterovirus D68 (EV-D68) is associated with a broad spectrum of illnesses, including mild to severe acute respiratory illness (ARI) and acute flaccid myelitis (AFM). Enteroviruses, including EV-D68, are typically detected in the United States during late summer through fall, with year-to-year fluctuations. Before 2014, EV-D68 was infrequently reported to CDC (1). However, numbers of EV-D68 detection have increased in recent years, with a biennial pattern observed during 2014-2018 in the United States, after the expansion of surveillance and wider availability of molecular testing. In 2014, a national outbreak of EV-D68 was detected (2). EV-D68 was also reported in 2016 via local (3) and passive national (4) surveillance. EV-D68 detections were limited in 2017, but substantial circulation was observed in 2018 (5). To assess recent levels of circulation, EV-D68 detections in respiratory specimens collected from patients aged <18 years* with ARI evaluated in emergency departments (EDs) or admitted to one of seven U.S. medical centers† within the New Vaccine Surveillance Network (NVSN) were summarized. This report provides a provisional description of EV-D68 detections during July-November in 2018, 2019 and 2020, and describes the demographic and clinical characteristics of these patients. In 2018, a total of 382 EV-D68 detections in respiratory specimens obtained from patients aged <18 years with ARI were reported by NVSN; the number decreased to six detections in 2019 and 30 in 2020. Among patients aged <18 years with EV-D68 in 2020, 22 (73%) were non-Hispanic Black (Black) persons. EV-D68 detections in 2020 were lower than anticipated based on the biennial circulation pattern observed since 2014. The circulation of EV-D68 in 2020 might have been limited by widespread COVID-19 mitigation measures; how these changes in behavior might influence the timing and levels of circulation in future years is unknown. Ongoing monitoring of EV-D68 detections is warranted for preparedness for EV-D68-associated ARI and AFM.

Shedding of Culturable Virus, Seroconversion, and 6-Month Follow-up Antibody Responses in the First 14 Confirmed Cases of Coronavirus Disease 2019 in the United States.

We aimed to characterize presence of culturable virus in clinical specimens during acute illness, and antibody kinetics up to 6 months after symptom onset, among 14 early patients with coronavirus disease 2019 in the United States. We isolated viable severe acute respiratory syndrome coronavirus 2 from real-time reverse-transcription polymerase chain reaction-positive respiratory specimens collected during days 0-8 after onset, but not after. All 13 patients with 2 or more serum specimens developed anti-spike antibodies; 12 developed detectable neutralizing antibodies. We did not isolate virus after detection of neutralizing antibodies. Eight participants provided serum at 6 months after onset; all retained detectable anti-spike immunoglobulin G, and half had detectable neutralizing antibodies. Two participants reported not feeling fully recovered at 6 months.

Patterns of Virus Exposure and Presumed Household Transmission among Persons with Coronavirus Disease, United States, January-April 2020.

We characterized common exposures reported by a convenience sample of 202 US patients with coronavirus disease during January-April 2020 and identified factors associated with presumed household transmission. The most commonly reported settings of known exposure were households and healthcare facilities; among case-patients who had known contact with a confirmed case-patient compared with those who did not, healthcare occupations were more common. Among case-patients without known contact, use of public transportation was more common. Within the household, presumed transmission was highest from older (>65 years) index case-patients and from children to parents, independent of index case-patient age. These findings may inform guidance for limiting transmission and emphasize the value of testing to identify community-acquired infections.

Risk factors for hospitalization among persons with COVID-19-Colorado.

BACKGROUND: Most current evidence on risk factors for hospitalization because of coronavirus disease 2019 (COVID-19) comes from studies using data abstracted primarily from electronic health records, limited to specific populations, or that fail to capture over-the-counter medications and adjust for potential confounding factors. Properly understanding risk factors for hospitalization will help improve clinical management and facilitate targeted prevention messaging and forecasting and prioritization of clinical and public health resource needs. OBJECTIVES: To identify risk factors for hospitalization using patient questionnaires and chart abstraction. METHODS: We randomly selected 600 of 1,738 laboratory-confirmed Colorado COVID-19 cases with known hospitalization status and illness onset during March 9-31, 2020. In April 2020, we collected demographics, social history, and medications taken in the 30 days before illness onset via telephone questionnaire and collected underlying medical conditions in patient questionnaires and medical record abstraction. RESULTS: Overall, 364 patients participated; 128 were hospitalized and 236 were non-hospitalized. In multivariable analysis, chronic hypoxemic respiratory failure with oxygen requirement (adjusted odds ratio [aOR] 14.64; 95% confidence interval [CI] 1.45-147.93), taking opioids (aOR 8.05; CI 1.16-55.77), metabolic syndrome (aOR 5.71; CI 1.18-27.54), obesity (aOR 3.35; CI 1.58-7.09), age ≥65 years (aOR 3.22; CI 1.20-7.97), hypertension (aOR 3.14; CI 1.47-6.71), arrhythmia (aOR 2.95; CI 1.00-8.68), and male sex (aOR 2.65; CI 1.44-4.88), were significantly associated with hospitalization. CONCLUSION: We identified patient characteristics, medications, and medical conditions, including some novel ones, associated with hospitalization. These data can be used to inform clinical and public health resource needs.

Changes in Influenza and Other Respiratory Virus Activity During the COVID-19 Pandemic - United States, 2020-2021.

The COVID-19 pandemic and subsequent implementation of nonpharmaceutical interventions (e.g., cessation of global travel, mask use, physical distancing, and staying home) reduced transmission of some viral respiratory pathogens (1). In the United States, influenza activity decreased in March 2020, was historically low through the summer of 2020 (2), and remained low during October 2020-May 2021 (<0.4% of respiratory specimens with positive test results for each week of the season). Circulation of other respiratory pathogens, including respiratory syncytial virus (RSV), common human coronaviruses (HCoVs) types OC43, NL63, 229E, and HKU1, and parainfluenza viruses (PIVs) types 1-4 also decreased in early 2020 and did not increase until spring 2021. Human metapneumovirus (HMPV) circulation decreased in March 2020 and remained low through May 2021. Respiratory adenovirus (RAdV) circulated at lower levels throughout 2020 and as of early May 2021. Rhinovirus and enterovirus (RV/EV) circulation decreased in March 2020, remained low until May 2020, and then increased to near prepandemic seasonal levels. Circulation of respiratory viruses could resume at prepandemic levels after COVID-19 mitigation practices become less stringent. Clinicians should be aware of increases in some respiratory virus activity and remain vigilant for off-season increases. In addition to the use of everyday preventive actions, fall influenza vaccination campaigns are an important component of prevention as COVID-19 mitigation measures are relaxed and schools and workplaces resume in-person activities.

Characteristics and Risk Factors of Hospitalized and Nonhospitalized COVID-19 Patients, Atlanta, Georgia, USA, March-April 2020.

We compared the characteristics of hospitalized and nonhospitalized patients who had coronavirus disease in Atlanta, Georgia, USA. We found that risk for hospitalization increased with a patient's age and number of concurrent conditions. We also found a potential association between hospitalization and high hemoglobin A1c levels in persons with diabetes.

Symptom Profiles and Progression in Hospitalized and Nonhospitalized Patients with Coronavirus Disease, Colorado, USA, 2020.

To improve recognition of coronavirus disease (COVID-19) and inform clinical and public health guidance, we randomly selected 600 COVID-19 case-patients in Colorado. A telephone questionnaire captured symptoms experienced, when symptoms occurred, and how long each lasted. Among 128 hospitalized patients, commonly reported symptoms included fever (84%), fatigue (83%), cough (73%), and dyspnea (72%). Among 236 nonhospitalized patients, commonly reported symptoms included fatigue (90%), fever (83%), cough (83%), and myalgia (74%). The most commonly reported initial symptoms were cough (21%-25%) and fever (20%-25%). In multivariable analysis, vomiting, dyspnea, altered mental status, dehydration, and wheezing were significantly associated with hospitalization, whereas rhinorrhea, headache, sore throat, and anosmia or ageusia were significantly associated with nonhospitalization. General symptoms and upper respiratory symptoms occurred earlier in disease, and anosmia, ageusia, lower respiratory symptoms, and gastrointestinal symptoms occurred later. Symptoms should be considered alongside other epidemiologic factors in clinical and public health decisions regarding potential COVID-19 cases.

Lack of Serologic Evidence of Infection Among Health Care Personnel and Other Contacts of First 2 Confirmed Patients With COVID-19 in Illinois, 2020.

OBJECTIVES: Widespread global transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus causing coronavirus disease 2019 (COVID-19), continues. Many questions remain about asymptomatic or atypical infections and transmission dynamics. We used comprehensive contact tracing of the first 2 confirmed patients in Illinois with COVID-19 and serologic SARS-CoV-2 antibody testing to determine whether contacts had evidence of undetected COVID-19. METHODS: Contacts were eligible for serologic follow-up if previously tested for COVID-19 during an initial investigation or had greater-risk exposures. Contacts completed a standardized questionnaire during the initial investigation. We classified exposure risk as high, medium, or low based on interactions with 2 index patients and use of personal protective equipment (PPE). Serologic testing used a SARS-CoV-2 spike enzyme-linked immunosorbent assay on serum specimens collected from participants approximately 6 weeks after initial exposure to either index patient. The 2 index patients provided serum specimens throughout their illness. We collected data on demographic, exposure, and epidemiologic characteristics. RESULTS: Of 347 contacts, 110 were eligible for serologic follow-up; 59 (17% of all contacts) enrolled. Of these, 53 (90%) were health care personnel and 6 (10%) were community contacts. Seventeen (29%) reported high-risk exposures, 15 (25%) medium-risk, and 27 (46%) low-risk. No participant had evidence of SARS-CoV-2 antibodies. The 2 index patients had antibodies detected at dilutions >1:6400 within 4 weeks after symptom onset. CONCLUSIONS: In serologic follow-up of the first 2 known patients in Illinois with COVID-19, we found no secondary transmission among tested contacts. Lack of seroconversion among these contacts adds to our understanding of conditions (ie, use of PPE) under which SARS-CoV-2 infections might not result in transmission and demonstrates that SARS-CoV-2 antibody testing is a useful tool to verify epidemiologic findings.

Investigation and Serologic Follow-Up of Contacts of an Early Confirmed Case-Patient with COVID-19, Washington, USA.

We describe the contact investigation for an early confirmed case of coronavirus disease (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), in the United States. Contacts of the case-patient were identified, actively monitored for symptoms, interviewed for a detailed exposure history, and tested for SARS-CoV-2 infection by real-time reverse transcription PCR (rRT-PCR) and ELISA. Fifty contacts were identified and 38 (76%) were interviewed, of whom 11 (29%) reported unprotected face-to-face interaction with the case-patient. Thirty-seven (74%) had respiratory specimens tested by rRT-PCR, and all tested negative. Twenty-three (46%) had ELISA performed on serum samples collected ≈6 weeks after exposure, and none had detectable antibodies to SARS-CoV-2. Among contacts who were tested, no secondary transmission was identified in this investigation, despite unprotected close interactions with the infectious case-patient.

Exposures Before Issuance of Stay-at-Home Orders Among Persons with Laboratory-Confirmed COVID-19 - Colorado, March 2020.

On March 26, 2020, Colorado instituted stay-at-home orders to reduce community transmission of SARS-CoV-2, the virus that causes coronavirus disease 2019 (COVID-19). To inform public health messaging and measures that could be used after reopening, persons with laboratory-confirmed COVID-19 during March 9-26 from nine Colorado counties comprising approximately 80% of the state's population† (Adams, Arapahoe, Boulder, Denver, Douglas, El Paso, Jefferson, Larimer, and Weld) were asked about possible exposures to SARS-CoV-2 before implementation of stay-at-home orders. Among 1,738 persons meeting the inclusion criteria§ in the Colorado Electronic Disease Surveillance System, 600 were randomly selected and interviewed using a standardized questionnaire by telephone. Data collection during April 10-30 included information about demographic characteristics, occupations, and selected activities in the 2 weeks preceding symptom onset. During the period examined, SARS-CoV-2 molecular testing was widely available in Colorado; community transmission was documented before implementation of the stay-at-home order. At least three attempts were made to contact all selected patients or their proxy (for deceased patients, minors, and persons unable to be interviewed [e.g., those with dementia]) on at least 2 separate days, at different times of day. Data were entered into a Research Electronic Data Capture (version 9.5.13; Vanderbilt University) database, and descriptive analyses used R statistical software (version 3.6.3; The R Foundation).