2020 Preliminary Data

Each year CDC releases Active Bacterial Core surveillance (ABCs) data describing the burden and epidemiology of invasive disease due to group A Streptococcus, group B Streptococcus, Haemophilus influenzae, Neisseria meningitidis, and Streptococcus pneumoniae. This year CDC is releasing preliminary 2020 ABCs data along with summary statistics comparing ABCs pathogen-specific incidence rates during the pandemic period of March to December 2020 to the rates during the pre-pandemic period from January 2014 to February 2020*, along with interpretations of how pandemic-related factors may have impacted ABCs pathogen disease burden.

*Neisseria meningitidis was not included in this analysis due to small numbers of reported cases.

Key findings from 2020 ABCs surveillance data

In 2020, CDC observed historic decreases in the invasive bacterial disease burden caused by pathogens monitored by ABCs.

The COVID-19 pandemic and the associated mitigation measures implemented early in the pandemic, likely played a role in these decreases.

Changes in overall incidence of invasive bacterial infections during 10-month pandemic period (March–December 2020)
Changes in overall incidence of invasive bacterial infections during 10-month pandemic period (March–December 2020) **
Pathogen % 95% credible interval
Group A Streptococcus -28% (-11% to -40%)
Group B Streptococcus -12% (-7% to -16%)
Haemophilus influenzae -59% (-51% to -65%)
Streptococcus pneumoniae  -58% (-52% to -62%)

**All ages

Methods for estimating changes during the pandemic period

CDC defined the COVID-19 pandemic period of 2020 as March–December, based on when SARS-CoV-2 was recognized to have widespread circulation in the United States, and non-pharmaceutical interventions (e.g., social distancing resulting from remote work and school arrangements, mask wearing) were put in place. CDC used interrupted time series analysis through Autoregressive Integrated Moving Average models fit to monthly incidence rates between January 2014–February 2020 to generate predicted pathogen-specific monthly incidence rates for March–December 2020. The predicted rates were compared to observed rates using incidence rate ratios (IRR) and 95% credible intervals (CIs) for the pandemic period. IRRs and CIs are reported as percentage change (1-IRR). We plan to include additional months of the pandemic period in future analyses.

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Use Bact Facts Interactive Data Dashboard to view data from 2020 and years prior.

Group A Streptococcus (GAS)
  • After increasing each year since 2012, overall invasive GAS annual incidence decreased from 7.6 cases per 100,000 population in 2019 () to 6.1 in 2020 (); the lowest annual rate since 2016.
  • Monthly invasive GAS rates were 28% lower than predicted during the pandemic period (IRR 0.72, 95% CI 0.60–0.89). The percentage change was greatest for children ages 5–17 years (67% lower than predicted, 95% CI 46–77%). Among adults, the greatest declines were in those aged ≥65 years (35% lower, 95% CI 13–49%).
Percent change in incidence of invasive group A Streptococcus cases per 100,000 population/year in Active Bacterial Core surveillance areas, March-December 2020

Percent change in invasive GAS cases per 100,000 population/year, Mar-Dec 2020.

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Group B Streptococcus (GBS)
  • After increasing each year since 2014, overall invasive GBS annual incidence decreased from 9.9 cases per 100,000 population in 2019 () to 8.8 in 2020 (); the lowest annual rate since 2014.
  • Monthly invasive GBS rates were 12% lower than predicted during the pandemic period (IRR 0.88, 95% CI 0.84 –0.93). Among adults, the greatest declines were in those aged ≥65 years (15% lower, 95% CI 9–20%). No significant changes were observed for persons <50 years old, including invasive GBS disease among infants <90 days old.
Percent change in incidence of invasive group B Streptococcus cases per 100,000 population/year in ABCs areas, March-December 2020

Percent change in invasive GBS cases per 100,000 population/year, Mar-Dec 2020.

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Haemophilus influenzae (HFlu)
  • Overall invasive HFlu annual incidence dropped from 2.2 cases per 100,000 population in 2019 () to 1.1 in 2020 (); the lowest annual incidence recorded since ABCs began in 1997.
  • Monthly invasive HFlu rates were 59% lower than predicted during the pandemic period (IRR 0.41, 95% CI 0.35–0.49). The percentage change was greatest for children aged 65 years (66% lower, 95% CI 59-71%).
Percent change in incidence of invasive Haemophilus influenzae cases per 100,000 population/year in ABCs areas, March-December 2020

Percent change in invasive HFlu cases per 100,000 population/year, Mar-Dec 2020.

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Streptococcus pneumoniae (SPN)
  • After fluctuating between 9.1 and 9.9 from 2012 through 2018, overall invasive SPN annual incidence dropped from 9.2 cases per 100,000 population in 2019 () to 5.4 in 2020 ().
  • Monthly SPN rates were 58% lower than predicted during the pandemic period (IRR 0.42, 95% CI 0.37–0.47). The percentage change was greatest for children ages 5–17 years (82% lower than predicted, 95% CI 75-85%). Among adults, the greatest declines were in those aged ≥65 years (68% lower, 95% CI 63-71%).
Percent change in incidence of invasive Streptococcus pneumoniae cases per 100,000 population/year in ABCs areas, March-December 2020

Percent change in invasive SPN cases per 100,000 population/year, Mar-Dec 2020

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Interpreting 2020 changes

The decreases observed in 2020 were the largest single-year decreases in the incidence of group A Streptococcus, group B Streptococcus, Haemophilus influenzae, and Streptococcus pneumoniae with one exception: the introduction of pneumococcal conjugate vaccine (PCV7) among children <5 years old in 2000 was associated with a large drop in Streptococcus pneumoniae in 2001.

COVID-19-associated non-pharmaceutical interventions likely reduced invasive bacterial disease due to bacteria typically transmitted via respiratory droplets, such as Streptococcus pneumoniae, Haemophilus influenzae, and group A Streptococcus as well as those that can be transmitted via direct contact, such as group B Streptococcus​.

Widespread interventions to limit the spread of SARS-CoV-2, the virus that causes COVID-19, likely contributed to fewer exposures to ABCs pathogens. Beginning in March 2020, mitigation measures, such as school and workplace closures, cancellation of public events, and restrictions on gatherings, went into effect and drastically reduced in-person interactions.

Delayed healthcare-seeking, broader use of telehealth, limited clinical laboratory capacity, and other factors may have impacted the diagnosis of invasive bacterial infections and detection of cases. For example, emergency department visits decreased markedly early in the pandemic. ​

No. The pandemic and corresponding public health response make explaining changes in the observed incidences of invasive bacterial infections challenging. In addition to factors mentioned here, unknown factors might have contributed to fewer exposures, infections, and detections. ​Continued surveillance and laboratory characterization of ABCs pathogens may improve CDC’s understanding of how the pandemic affected the incidence of infections and may identify new prevention strategies.​

The number of infections reported to ABCs decreased in 2020. CDC is confident that this reflects true decreases in invasive bacterial disease identified by laboratory-based isolation of ABCs pathogens from a normally sterile site and are not due to changes in surveillance methods.