Impact of COVID-19 on Infectious Diseases and Public Health

Feb. 8, 2022

Treponema pallidum, the causative agent of syphilis.
Treponema pallidum, the causative agent of syphilis.

The COVID-19 pandemic has had both negative and positive impacts on infectious diseases of public health importance. Shifting public health resources to COVID-19 detection, control and prevention has negatively impacted STD control efforts. While COVID-19 mitigation strategies, particularly mask wearing, physical distancing, school closures and limiting travel and economic activity, have resulted in a significant decline in 2 of the most clinically important endemic respiratory viruses—influenza and respiratory syncytial virus (RSV). Perhaps more surprising has been a significant decline in Norovirus infections, a diarrheal pathogen. Collectively, the pandemic has had a profound impact on the public health profession.

Impact on Public Health Profession

The COVID-19 pandemic has put extraordinary pressure on U.S. public health professionals. A survey of over 26,000 U.S. public health workers, conducted in spring 2021, reported that 90% of participants spent at least some time on the COVID-19 public health response, while slightly more than 50% spent more than half of their work time on COVID-19-related activities; 59% worked over 40 hours per week, and 12% worked more than 60 hours per week on COVID-19-related activities. This is occurring in an environment where retirements are common and staffing and pay levels are low. Not surprisingly, mental health issues among these workers are disturbingly high. For those individuals working more than 40 hours per week, 63% reported depression and anxiety while over 90% felt moral injury.

To further complicate this already discouraging picture, close to half felt underappreciated at work and disconnected from family and friends because of their jobs. Perhaps most disconcerting is that 12% received work-related threats, while 23% felt bullied or harassed. With an overworked, under-resourced, discouraged public health work force focused primarily on COVID-19, what has been the impact on public health control efforts for other infectious agents?

Sexually Transmitted Diseases (STDs)

One of the key activities of public health professionals is the control of STDs. Pre-pandemic, a consistent rise in STDs was observed in the latter half of the previous decade. This rise is clearly multi-factorial, but under-resourced public health clinics and laboratories clearly contributed to this rise.

Reported new STD cases per year from 2014 to 2019.
Reported new STD cases per year from 2014 to 2019.

As STD screening personnel were shifted to COVID-19 control duties during the early stages of the pandemic, there was a significant dip in STD cases, especially during the stay-at-home orders of March-May 31, 2020. This was almost certainly due to documented reduced STD testing that occurred during that period because of reduced clinic hours and testing backlogs. However, according to data published by the CDC, the weekly reported U.S. cases of chlamydia, gonorrhea and syphilis began to resurge in early May 2020, prior to the end of the stay-at-home order.

Screening of patients for both chlamydia and gonorrhea was further complicated by a shortage of testing reagents during the summer and fall of 2020. While the adverse consequences of a lack of testing reagents is currently unknown, undiagnosed, and thus untreated, chlamydia and gonorrhea infections are important causes of female infertility.

Weekly reported STD cases in 2020 compared to 2019.
Weekly reported STD cases in 2020 compared to 2019.

Congenital Syphilis

Syphilis is a bacterial infection caused by Treponema pallidium. Congenital syphilis, where the bacterium is transmitted from mother to child, either during pregnancy or at birth, has been on the rise in the U.S. over the past decade. Pregnant women with primary or secondary syphilis can transmit the organism at any stage of pregnancy. The outcome of this infection is dependent on when, and for how long, the mother has been infected, and the stage of pregnancy at which the fetus is infected. It is the greatest contributor to years of lost life due to syphilis and was projected to be responsible for 140 deaths in 2020. Perinatal death occurs in up to 40% of cases when the mother is untreated. Surviving infants can have a variety of complications, including low birth weight, developmental delay, skeletal abnormalities, meningitis, hearing and vision deficits, enlarged liver and spleen and anemia.

One of the consequences of the COVID-19 pandemic has been a decrease in pre-natal public health services for marginalized populations as public health personnel are shifted to COVID-19 screening and vaccination. Pre-natal care is essential for the prevention of congenital syphilis. In particular, maternal syphilis screening should be done at the initial visit, and, if the patient is in a high-risk group, testing should be repeated (at minimum) at the beginning of the third trimester. Seropositive women can be treated with a single injection of benzathine penicillin, effectively preventing congenital syphilis. Globally, congenital syphilis has been eliminated from 5 countries, proving that aggressive public health intervention can work. However, the shifting of scarce public health resources to COVID-19 control likely will result in increasing years of life lost to congenital syphilis in the years to come.

Syphilis and HIV

Syphilis is well recognized as a significant risk factor for the acquisition of HIV, and studies show that the incidence has increased dramatically over the past decade among gay, bisexual and men who have sex with men (MSM). The skin ulcers (chancre) found in primary syphilis increase the risk of HIV transmission in 2 ways. First, ulceration of the epithelium allows the virus to penetrate to underlying tissue. Second, the ulcerated underlying tissue is rich in activated lymphocytes and macrophages, which are the key target cells for HIV infection./p>

Controlling cases of syphilis is therefore considered an important intervention in controlling the spread of HIV. However, there is growing concern that shifting STD prevention resources to COVID-19 prevention and control will result in further increases in syphilis cases that consequently lead to increases in HIV infection. It is estimated that in 2019, 13% of people living with HIV (PLWH) were not aware of their infection status. The number of HIV tests performed in a clinical setting during the 2020 stay-at-home order declined between by 68%-97% in 4 U.S. metropolitan areas. In those same areas, the number of HIV tests performed during the period immediately following the stay-at-home order was still 11%-54% below historic data. This decline in testing will likely increase the number of people who are unaware of their positive HIV status. This is associated with higher rates of HIV transmission, delays in treatment and progression to AIDS.

Respiratory Infections

Specific public health mitigations have been used to try to control the spread of COVID-19. These mitigations are aimed at preventing the transmission of respiratory pathogens (especially viruses) spread by droplets. There are different tiers of mitigation. Mask wearing, physical distancing and quarantining the infected represent first tier activities. While second tier activities are aimed at reducing viral transmission by limiting travel, either locally by limiting public transportation, or at greater distances by bus, train, plane and boats. Third tier activities, in which all but essential societal interactions are curtailed, or "locked down," occurred in the U.S. between March and May 31, 2020. This lock down resulted in large numbers of people working from home, while day care centers, schools and all but essential businesses were shuttered.

While some mitigations have been controversial, especially mask-wearing and school closures, their impact on the spread of other respiratory viruses, especially respiratory syncytial virus (RSV) and influenza virus, was striking. Between Oct. 2020 and May 2021, there were 0.3 cases/100,000 RSV hospitalizations, compared to 27.1 and 33.4 cases/100,000 in the previous 2 years. The story was similar for the flu virus. There were 0.8/100,000 flu hospitalizations in the northern hemisphere, compared to 62-109/1 million flu hospitalizations during the previous 4 flu seasons. Flu hospitalization rates in the 2021-2022 season have rebounded from 2020-2021 lows to 2.6/100,000 as of Jan. 1, 2022 but are still historically low.

These data must be viewed cautiously since the height of flu season typically peaks between mid-Jan. to mid-March in the U.S. In addition, data not yet peer-reviewed suggest that there is a significant mismatch between the H3N2 variant present in the 2021-2022 flu vaccine and the H3N2 variant that is currently circulating, suggesting the potential for immune escape by the circulating H3N2 variant.

Comparison of cumulative rate of laboratory confirmed influenza hospitalizations.
Comparison of cumulative rate of laboratory confirmed influenza hospitalizations.

The combination of immune escape by the circulating H3N2 flu variant and the raging epidemic of the SARS-CoV-2 Omicron variant has led to concerns in the popular press about a "flurona" epidemic," where individuals may become infected with both flu and Omicron at the same time. For now, there have been only a handful of coinfected people globally, and with Omicron cases rapidly declining in the U.S. and influenza cases remaining low, it appears that threat is likely also declining. First level mitigation practice—mask wearing, physical distancing, avoiding crowded settings—will protect against the combination of these viruses.


Early in the pandemic, stores were emptied of bleach and disinfectants. "Wash your hands for 30 seconds," was a commonly heard mantra. Concerns that SARS-CoV-2 might be spread by "fomite" transmission made "deep cleaning" a key pandemic catch phrase and control strategy.

There is little evidence that SARS-CoV-2 is spread through surface contact, however these sanitary practices are important to the prevention of many pathogens, including foodborne viruses and bacteria. This emphasis on environmental cleaning combined with the closing of schools, day care centers and docking of most cruise ships globally has resulted in a sufficient decline in Norovirus outbreaks in the U.S.

Number of Suspected or Confirmed Norovirus Outbreaks Reported by NoroSTAT-Participating States Per Week, 2012-2022.
Number of Suspected or Confirmed Norovirus Outbreaks Reported by NoroSTAT-Participating States Per Week, 2012-2022.

On March 11, 2020, the World Health Organization (WHO) declared COVID-19 to be pandemic. Over the past 22 months, the public health community in the U.S. has played a key role in combating this scourge. Their underappreciated efforts have consequently led to significant mental health issues forcing some from the profession and overwhelming others. COVID-19 has resulted in a worsening crisis in the control of sexually transmitted disease while at the same time have mitigated other public health problems such as flu, RSV, and norovirus disease outbreaks. If nothing else, this pandemic has reminded us of the important role that this "invisible army" of dedicated professionals play every day in protecting us from plagues and pestilence.

Author: Peter Gilligan, Ph.D., D(ABMM), F(AAM)

Peter Gilligan, Ph.D., D(ABMM), F(AAM)
Peter Gilligan, Ph.D., D(ABMM), F(AAM) is the former Director of the Clinical Microbiology-Immunology Laboratories at the University of North Carolina Hospitals.