CDC Report Addresses Mardi Gras Impact — And The Fact That No One Was Canceling Events In February

Apr 13, 2020

The Centers for Disease Control and Prevention on Friday released a report packed with data on the spread of COVID-19.

First, here's what you came for:

Because COVID-19 is primarily transmitted by respiratory droplets, population density might also play a significant role in the acceleration of transmission. Cumulative incidence in urban areas like NYC and DC exceeds the national average. Louisiana, which experienced a temporarily high population density because of an influx of visitors during Mardi Gras celebrations in mid-February, has a higher cumulative incidence and greater increase in cumulative incidence than other states in the South. Mardi Gras, which concluded on February 25, occurred at a time when cancelling mass gatherings (e.g., festivals, conferences, and sporting events) was not yet common in the United States.

The meat of the report shows Louisiana among the states with the highest cumulative incidence.

What does that mean? Have a gulp of your coffee...

The CDC defines cumulative incidence, also referred to as incidence proportion, as "the proportion of an initially disease-free population that develops disease, becomes injured, or dies during a specified (usually limited) period of time."

So that's: Number of new cases of disease or injury during specified period divided by size of population at start of period.

(Weird how much we're all learning about epidemiology, huh?)

This report includes cumulative incidence on March 31 and April 7. 

As of April 7, a total of 395,926 COVID-19 cases were reported in the United States (Table). Cases were reported by all 50 states, DC, NYC, Guam, the Northern Mariana Islands, Puerto Rico, and the U.S. Virgin Islands. Two thirds of all COVID-19 cases (66.7%) were reported by eight jurisdictions: NYC (76,876), New York (61,897), New Jersey (44,416), Michigan (18,970), Louisiana (16,284), California (15,865), Massachusetts (15,202), and Pennsylvania (14,559) (Figure 1). The overall cumulative COVID-19 incidence in the United States was 119.6 cases per 100,000 population on April 7 (Table). Among jurisdictions in the continental United States, cumulative incidence was lowest in Minnesota (20.6) and highest in NYC (915.3). Nine reporting jurisdictions had rates above the national rate: NYC (915.3), New York (555.5), New Jersey (498.6), Louisiana (349.4), Massachusetts (220.3), Connecticut (217.8), Michigan (189.8), DC (172.4), and Rhode Island (133.7).

(Emphasis ours.)

The report also measures absolute seven-day changes in cumulative incidence , which "were calculated by subtracting the jurisdiction-specific cumulative incidence on March 31 from that observed on April 7."

During March 31–April 7, the overall cumulative incidence of COVID-19 increased by 63.4 cases per 100,000 (Table). This increase ranged from 8.3 in Minnesota to 418.0 in NYC. During the 7-day period, increases in 11 jurisdictions exceeded the national increase: NYC (418.0), New Jersey (288.7), New York (262.4), Louisiana (237.1), Connecticut (130.2), Massachusetts (124.3), Michigan (113.6), DC (101.9), Rhode Island (84.6), Pennsylvania (75.9), and Maryland (64.0) (Figure 2).

(Again, emphasis ours.)

Cumulative incidence of COVID-19, by report date — selected U.S. jurisdictions, March 10–April 7, 2020. Cases per 100,000 population. Restricted to the 11 jurisdictions reporting the largest absolute increase in COVID-19 cumulative incidence during the most recent 7-day reporting period, March 31-April 7, 2020. Data from New York are exclusive of New York City.
Credit Centers for Disease Control and Prevention

OK, one last bit on Louisiana:

By April 7, 55 (98.2%) of the 56 jurisdictions reporting COVID-19 cases also reported at least one related death (Table); however, approximately half (52.7%) of all deaths (12,757) were reported from three jurisdictions: NYC (4,111), New York (1,378), and New Jersey (1,232) (Figure 3). Other jurisdictions reporting ≥300 deaths included Michigan (845), Louisiana (582), Washington (394), Illinois (380), California (374), Massachusetts (356), and Georgia (351). Case-fatality ratios ranged from 0.7% in Utah to 5.7% in Kentucky.

(Emphasis, once again, ours.)

You can read the full report here.

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