Infectious Disease Updates
December 1, 2025
By Carol A. Kemper, MD, FIDSA
Lyme Disease: 2022 Reporting Requirements
Sources: Kugeler KJ, Earley A, Mead PS, Hinckley AF. Surveillance for Lyme disease after implementation of a revised case definition — United States, 2022. MMWR Morb Mortal Wkly Rep. 2024;73(6);118-123.
Centers for Disease Control and Prevention. Lyme disease surveillance and data. March 13, 2025. https://www.cdc.gov/lyme/data-research/facts-stats/index.html
Lyme disease has been a reportable condition in the United States since 1991. Prior to the disruption in government functioning, the Centers for Disease Control and Prevention (CDC) had been working to improve Lyme disease surveillance and reporting. Cases are reported to the National Notifiable Disease Surveillance System (NNDSS) by state and local health departments and the District of Columbia, and previously both more extensive clinical data and laboratory confirmation were required. It was suspected this requirement curbed active reporting. Thus, in January 2022, the case definition and reporting requirements were revised based on laboratory data alone. In addition, improved testing methods were approved by the Food and Drug Administration (FDA) in 2019, using a modified two-tiered testing method (MTTT), increased the specificity and sensitivity of antibody detection, especially during early disease.
As a result of these changes, there has been a sharp increase in reported cases of Lyme disease in the United States. A total of 62,551 and 89,486 cases of Lyme were reported to the CDC in 2022 and 2023, respectively. These data represent a 1.7 to 2.4 times increase in cases compared with the average annual number of cases reported in the three years prior to these changes (2017-2019). While these numbers are concerning on the surface, it is important to recognize that it likely reflects the recent changes in surveillance testing and reporting — and not an increase in disease risk.
More than 90% of all Lyme cases are reported by 15 high-incidence jurisdictions in the Northeast, mid-Atlantic, and Upper Midwest. Peak onset of cases occurs in late June to early July. Newer reporting requirements are based on the date of diagnosis or laboratory confirmation, and not the onset of symptoms (as before), and thus the reported peak incidence in cases is now occurring about two weeks later than previously. More than half of cases historically occur in males (~57%).
Cases of suspected early Lyme disease based on clinical symptoms and a likely “falsely negative” test still may be reported. Despite recent changes in reporting requirements, there is significant underreporting of cases, and some estimate that nearly 500,000 cases of Lyme occur annually in the United States, if suspect cases and cases with presumptive treatment are included.
In my experience, clinicians too often forget that Lyme serologies are negative in 60% to 70% of early cases of Lyme disease, since it is too early in the disease course to have mounted an antibody response. By reinforcing the need for a confirmatory laboratory test, I hope this revised case definition does not contrarily discourage clinicians from recognizing and providing treatment to early cases. Early Lyme symptoms occurring within three to 30 days of a tick bite often are nonspecific and include flu-like symptoms, fever, and headache. The accompanying erythema migrans (EM) rash occurs in many patients (40% to 80%) but not all. And the EM rash may not take on the characteristic “bull’s eye” appearance with central clearing — generally appears as an erythematous round or oval that may slowly expand over several days. That latter finding may be the difference between Lyme and a spider bite. The clinical presentation combined with appropriate risk factors should be a trigger for treatment — not waiting for a positive blood test.
Pregnant Women Must Be Screened for Syphilis
In 2023, syphilis cases reached their highest number in the United States since the 1950s. While there was a brief dip in cases during the first few months of social isolation with COVID-19, cases have more than doubled since 2015. Testing those who present with symptoms or other sexually transmitted infections (STIs) has not been sufficient to curb this upward trend.
Untreated syphilis during pregnancy can result in severe fetal infection, unbeknownst to the mother and the treating physician, with significant morbidity and mortality for the infant. Up to 40% of babies born with congenital syphilis may be stillborn or die shortly after birth. Those who survive may have deformed bones, vision and hearing loss, and permanent neurologic deficits. In 2023, the highest number of congenital syphilis cases was reported to the Centers for Disease Control and Prevention (CDC) in 30 years: 3,882 cases of congenital syphilis occurred; 279 were born stillborn or died.1 Cases in live births to Black women and in Native American/Alaska Native women outstripped cases in white women by 3.9-11.9 times, respectively.
Importantly, recent 2022 data found that 197 cases of congenital syphilis (5%) occurred in late pregnancy after a negative screening test in early pregnancy.
Syphilis surveillance during pregnancy is imperfect.1 Forty-three states and the District of Columbia have required prenatal screening, but the regulatory requirements vary and recommended testing times differ between states: 86% require first-trimester screening; 39% require third-trimester screening; 6% require first-trimester screening along with late-trimester screening for those at risk; and a few require testing at the time of delivery. However, prenatal care is haphazard in this country, especially for women with mental health issues or substance abuse, and screening is not always done. And there are no penalties for failure to screen.
In August 2023, the U.S. Department of Health and Human Services created a National Syphilis and Congenital Syphilis Syndemic (NSCSS) Federal Task Force to investigate and combat the factors contributing to the syphilis epidemic. The use of the word syndemic was telling, indicating the federal government’s acknowledgment of the importance of such social factors as sexual behavior coupled with drug use and mental health, and homelessness.
As a result, the U.S. Preventive Services Task Force has created newer guidance for states that require universal screening for syphilis infection during pregnancy, recommending that all women should be tested for syphilis when they first present for care.2 If testing has not been done early in pregnancy, it should be done at the first opportunity. Although we are experiencing a shortage, the CDC continues to recommend penicillin G as the only treatment for syphilis in pregnancy. The California Department of Public Health (CDPH) has taken these recommendations a step further and recommended that pregnant women be screened three times during pregnancy — at the first prenatal encounter, early in the third trimester (at 28 weeks gestation or thereafter), and at delivery. Those with signs or symptoms of syphilis (primary or secondary infection) should receive preemptive empiric treatment for early stage disease before waiting for confirmatory serologic test results.
References
1. Centers for Disease Control and Prevention, Division of STD Prevention. State statutory and regulatory language regarding prenatal syphilis screenings in the United States. Aug. 29, 2025; https://www.cdc.gov/syphilis/media/pdfs/2025/09/Prenatal-Syphilis-Screening-Laws-2025.pdf
2. US Preventive Services Task Force; Silverstein M, Wong JB, Davis EM, et al. Screening for syphilis infection during pregnancy. US Preventive Services Task Force Reaffirmation Recommendation Statement. JAMA. 2025;333(22):2006-2012.
Pacific Coast Tick Fever — Not Just Another Rickettsial Spotted Fever? Or Is It?
Source: Paddock CD, Karpathy SE, Henry A, et al. Rickettsia rickettsii subsp californica subsp nov, the etiologic agent of Pacific Coast Tick Fever. J Infect Dis. 2025;231:849-858.
I have always loved reading about rickettsial infections, and it seemed cool that my home state of California had its own distinct rickettsial species, separate from Rickettsia rickettsii (the causative agent of Rocky Mountain spotted fever [RMSF]). Our unique strain of Rickettsia was first isolated in 1966 from the Pacific Coast tick Dermacentor occidentalis. And as early as the 1980s, it was clear that some cases of RMSF-like illness were caused by an unclassified rickettsial serotype, designated as Rickettsia 364D. For many years, serologic assays have been able to distinguish Rickettsia 364D from R. rickettsii. Earlier multilocus sequence typing methods suggested Rickettsia 364D was distinguishable but likely formed a subspecies within the genus R. rickettsii.
These authors provided an integrative approach, comparing phenotypic, ecological, and clinical data combined with whole-genome sequencing (WGS) of 11 strains of Rickettsia 364D, and comparing them with 14 strains of R. rickettsii. The 11 364D strains came from multiple locations in California across 800 km and more than 50 years apart. Although WGS demonstrated consistent genetic differences between these two groups of bacteria, with some unique coding genes, smaller gene insertions and deletions, and single nucleotide polymorphisms, it appears that Rickettsia 364D forms a distinct phylogenetic clade within R. rickettsii, with 11 distinct subclades that confirm their geographic origins within California. As such, the authors proposed designating 364D as Rickettsia rickettsii subsp californica. All southern California 364D isolates formed one monophyletic clade, while all but one of the northern California isolates fell into a second monophyletic clade. One clade from Lake County in northern California was an outgroup.
Despite these genetic similarities, there are some intriguing differences between Rickettsia 364D and R. rickettsii (RMSF). Rickettsia 364D is found exclusively in the Dermacentor occidentalis tick in California. The illness associated with Rickettsia 364D commonly causes one or more eschars and regional lymphadenopathy, as well as moderately high fever, headache, malaise, and sometimes cytopenias. Maculopapular rash occurred in two of four (50%) children described in one study and two of 14 (14%) patients described elsewhere in 2016. In this latter report, hospitalization was infrequent and there were no deaths.
In contrast, R. rickettsii is found in multiple tick species in several regions of the United States. RMSF is characterized by maculopapular or petechial rash in more than 90% of patients, including rash on the palms and soles. Regional lymphadenopathy and eschar are less common. RMSF is more frequently fatal, with an overall case fatality rate of 10%, but mortality may be higher (30% to 70%) in untreated cases.
Carol A. Kemper, MD, FIDSA, is Medical Director, Infection Prevention, El Camino Hospital, Palo Alto Medical Foundation.
Lyme Disease; Pregnant Women Must Be Screened for Syphilis; Pacific Coast Tick Fever
You have reached your article limit for the month. Subscribe now to access this article plus other member-only content.
- Award-winning Medical Content
- Latest Advances & Development in Medicine
- Unbiased Content