On January 25, 2022 this report was posted as an MMWR Early Release on the MMWR website (https://www.cdc.gov/mmwr).The B.1.1.529 (Omicron) variant of SARS-CoV-2, the virus that causes COVID-19, was first clinically identified in the United States on December 1, 2021, and spread rapidly. By late December, it became the predominant strain, and by January 15, 2022, it represented 99.5% of sequenced specimens in the United States* (1). The Omicron variant has been shown to be more transmissible and less virulent than previously circulating variants (2,3). To better understand the severity of disease and health care utilization associated with the emergence of the Omicron variant in the United States, CDC examined data from three surveillance systems and a large health care database to assess multiple indicators across three high-COVID-19 transmission periods:

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Rationale: Persons with cystic fibrosis (CF) are at high risk of nontuberculous mycobacterial (NTM) infection, with treatment requiring prolonged multidrug regimens that include macrolides. Although macrolides, specifically azithromycin, are used in the management of patients with CF with chronic Pseudomonas, macrolide-resistant NTM infections are of growing concern. Objectives: To evaluate the relationship between chronic macrolide use and NTM infection among patients with CF included in the 2011 CF Patient Registry (CFPR). Methods: We performed a nested case-control study: incident NTM cases were persons aged more than 5 years with at least one positive culture for NTM in 2011. Controls were persons with negative cultures in 2010 and 2011. Measurements and Main Results: The 2011 CFPR included 27,112 patients; 5,403 (20%) were cultured for mycobacteria in 2010-2011 and met all inclusion criteria. Of these, 191 (4%) were NTMpositive in 2011 only (cases); 5,212 (96%) were NTM-negative in 2010 and 2011 (control subjects). Among the cases, 122 (64%) were culture-positive for Mycobacterium avium complex (MAC) and 69 (36%) for M. abscessus. Azithromycin use in 2010 was less frequently reported among MAC cases (57%; odds ratio ¼ 0.7, P , 0.05) and M. abscessus cases (51%; odds ratio ¼ 0.5, P , 0.01) than in control subjects (66%). Among adolescents and adults, patients with the greatest number of years on chronic macrolides were the least likely to develop incident NTM in 2011 (P , 0.01). Conclusions: Patients with incident NTM infections from either MAC or M. abscessus were less likely to have had chronic azithromycin treatment in the past year. However, because macrolide monotherapy may lead to macrolide resistance, routine screening for NTM should be considered for persons with CF. Keywords: macrolides; cystic fibrosis; nontuberculous mycobacteriaPersons with cystic fibrosis (CF) are at significantly greater risk of contracting nontuberculous mycobacterial (NTM) infections than the general population, with an estimated disease prevalence of 13-23% among all patients with CF (1, 2). Furthermore, recent research demonstrates that NTM is prevalent in CF populations globally (3-6), with Mycobacterium avium complex (MAC) and Mycobacterium abscessus being the most commonly isolated species from patients with CF in the United States (1, 7). After an NTM infection is established in the airways of persons with CF, eradication is difficult and often requires prolonged use of multidrug treatment regimens that include a macrolide (8, 9), the only drugs for which in vitro susceptibility correlates with clinical outcomes and treatment response for NTM infections (8, 10). However, macrolides are also increasingly used for the general management of CF because of their antiinflammatory properties (11), raising concerns over the potential development of macrolide-resistant NTM infections from long-term macrolide use.Macrolide-resistant pulmonary NTM infections in patients with CF are even more difficult to treat and have been associ...