Volume 29, Number 4—April 2023
Research
Outbreaks of SARS-CoV-2 Infections in Nursing Homes during Periods of Delta and Omicron Predominance, United States, July 2021–March 2022
, Amelia A. Keaton, Lucas G. Ochoa, Kelly M. Hatfield, Paige Gable, Kelly A. Walblay, Richard A. Teran, Meghan Shea, Urooj Khan, Ginger Stringer, Meenalochani Ganesan, Jordan Gilbert, Joanne G. Colletti, Erin M. Grogan, Carly Calabrese, Andrew Hennenfent, Rebecca Perlmutter, Katherine A. Janiszewski, Christina Brandeburg, Ishrat Kamal-Ahmed, Kyle Strand, Matthew Donahue, M. Salman Ashraf, Emily Berns, Jennifer MacFarquhar, Meghan L. Linder, Dat J. Tran, Patricia Kopp, Rebecca M. Walker, Rebekah Ess, James Baggs, John A. Jernigan, Alex Kallen, Jennifer C. Hunter, and Monitoring Outbreaks of Variants in Nursing Homes (MOVIN) Surveillance Team1
Table
Descriptive characteristics of eligible nursing home outbreaks (N = 1,247), by period of SARS-CoV-2 variant predominance, United States, July 2021–January 2022*
| Characteristic | Outbreaks beginning during Jul 26–Nov 1: Delta period |
Outbreaks beginning during Nov 2–Dec 18: mixed Delta/Omicron period |
Outbreaks beginning during Dec 19–Jan 31: Omicron period |
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|---|---|---|---|---|---|---|
| No. outbreaks (% total) |
356 (29) |
355 (28) |
536 (43) |
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| Individual skilled nursing facilities |
347 |
351 |
536 |
|||
| Active outbreaks per week, median (IQR) |
146 (100–163) |
178 (161–237) |
697 (470–838) |
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| Jurisdiction | ||||||
| Chicago | 8 (2.2) | 51 (14.3) | 22 (4.1) | |||
| Colorado | 63 (17.7) | 53 (14.9) | 108 (20.1) | |||
| Connecticut | 33 (9.3) | 38 (10.7) | 56 (10.5) | |||
| Iowa | 3 (0.8) | 1 (0.3) | 1 (0.2) | |||
| Maryland | 61 (17.1) | 92 (25.8) | 35 (6.5) | |||
| Massachusetts | 40 (11.2) | 71 (19.9) | 184 (34.4) | |||
| Nebraska | 18 (5.1) | 2 (0.6) | 2 (0.4) | |||
| North Carolina | 38 (10.7) | 15 (4.2) | 21 (3.9) | |||
| Oregon | 36 (10.1) | 10 (2.8) | 34 (6.4) | |||
| South Carolina | 34 (9.6) | 12 (3.4) | 30 (5.6) | |||
| Utah |
22 (6.2) |
10 (2.8) |
43 (8.0) |
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| SARS-CoV-2 outbreak variant identified among >1 resident | ||||||
| Delta, B.1.672 and AY.1-AY.107 lineages | 176 (49.4) | 60 (16.9) | 4 (0.7) | |||
| Omicron, B.1.1.529, BA.1, BA.2 lineages | 4 (1.1) | 50 (14.0) | 194 (36.3) | |||
| Alpha | 1 (0.3) | 0 | 0 | |||
| Other | 2 (0.6) | 1 (0.3) | 0 | |||
| Multiple variants identified | 6 (1.7) | 31 (8.7) | 10 (1.9) | |||
| No sequencing information available |
167 (46.9) |
213 (59.8) |
328 (61.3) |
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| Initial infection in the outbreak | ||||||
| Staff | 220 (61.8) | 226 (63.5) | 391 (73.1) | |||
| Resident | 110 (30.9) | 100 (28.1) | 77 (14.4) | |||
| Both staff and resident infections at onset | 26 (7.3) | 29 (8.2) | 67 (12.5) | |||
| Unknown or missing |
0 |
0 |
1 (0.2) |
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| Days from initial infection to subsequent resident infection in index cluster, median (IQR) |
4 (0–11) |
5 (0–16) |
4 (0–9) |
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| Median resident census at outbreak onset per outbreak† | ||||||
| Total no. residents (IQR) | 89 (59–114) | 98 (74–129) | 79 (54–106) | |||
| Residents with booster dose % (IQR)‡ | 0.0 (0–0) | 55.7 (28–75) | 74.0 (56–86) | |||
| Residents with primary vaccine series alone, % (IQR) | 90.0 (81–96) | 38.0 (21–79) | 21.0 (11–35) | |||
| Residents partially vaccinated, % (IQR) | 1.0 (0–3) | 1.0 (0–2.3) | 0.0 (0–1.8) | |||
| Residents unvaccinated, % (IQR) |
7.0 (3–13) |
5.5 (3–11) |
5.0 (2–9) |
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| Median resident infections in first 28 d per outbreak§ | ||||||
| No. infected residents (IQR) | 4 (0–10) | 6 (1–14) | 10 (4–20) | |||
| Infected residents with booster dose, % (IQR)‡ | 0.0 (0–0) | 0.0 (0–18) | 35.7 (11–59) | |||
| Infected residents with primary vaccine series alone, % (IQR) | 87.5 (71–100) | 75.0 (46–100) | 46.2 (27–67) | |||
| Infected residents without vaccination, % (IQR) |
5.3 (0–25) |
8.7 (0–23) |
5.0 (0–17) |
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| Outbreak duration | ||||||
| <28 d | 85 (23.9) | 26 (7.3) | 16 (3.0) | |||
| 29–41 d | 93 (26.1) | 23 (6.5) | 71 (13.3) | |||
| >42 d |
178 (50.0) |
306 (86.2) |
449 (83.8) |
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| Outbreak status at end of infection surveillance period¶ | ||||||
| Closed | 340 (95.5) | 308 (86.8) | 474 (88.4) | |||
| Still active | 16 (4.5) |
47 (13.2) |
62 (11.6) |
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*Values are no. (%) except as indicated. Dates of variant predominance were July 26–November 1, 2021 (Delta), November 2–December 18, 2021 (mixed Delta/Omicron), and December 19, 2021–January 31, 2022 (Omicron). †Resident census data were incomplete for 114 (32%) (Delta period), 133 (37%) (mixed Delta/Omicron period), and 247 (46%) (Omicron period) outbreaks. As a result, denominators used for median resident census at outbreak onset were 242 (Delta), 222 (mixed Delta/Omicron), and 289 (Omicron). ‡Residents who received a booster dose could not be distinguished from residents who received additional vaccine dose. §Infection attack rates were restricted to resident infections present at outbreak onset and those infected within first 28 days of outbreak; all outbreaks included in this analysis had at least 28 days for case ascertainment. ¶All outbreaks included in analysis began before February 1, 2022. Resident infections were reported through February 28, 2022, making March 14, 2022, the last day for an outbreak to close (2 weeks with no infections among residents or staff).
1Additional members of the MOVIN Surveillance Team are listed at the end of this article.