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Reportable medical events at Military Health System facilities, second quarter, 2026

Image of MSMR 202610 Photo4. In the second quarter of 2026, norovirus, campylobacteriosis, and giardiasis were the most frequently reported gastrointestinal illnesses among U.S. active component service members.

10/1/2026 By: Matthew W. R. Allman, MPH; Anthony R. Marquez, MPH; Katherine S. Kotas, MPH; Kiara Scatliffe-Carrion, MPH

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Reportable Medical Events (RMEs) are documented in the Disease Reporting System internet (DRSi) by health care providers and public health officials throughout the Military Health System (MHS) for monitoring, controlling, and preventing the occurrence and spread of diseases of public health interest or readiness importance. These reports are reviewed by a team of validators from Defense Centers for Public Health (DCPH). The DRSi collects reports on over 70 different RMEs, including infectious and non-infectious conditions, outbreak reports, sexually transmitted infection (STI) risk surveys, and tuberculosis contact investigation reports. A complete list of RMEs is available in the 2022 Armed Forces Reportable Medical Events Guidelines and Case Definitions.1 Data reported in these tables are considered provisional and do not represent conclusive evidence until case reports are fully validated.

Total cases among active component service members (ACSMs) reported per week are displayed in the graph for the 5 RMEs for the prior year, or preceding 52 weeks. Each quarter, the graph is updated and presented with the quarter’s (Q2, 2026) 5 most frequently reported RMEs, which may differ from previous quarters.

FIGURE 1. Leading Five Reportable Medical Events by Calendar Week, Active Component, U.S. Armed Forces, June 29, 2025–June 30, 2026 This line graph, plotted on a logarithmic vertical axis ranging from 1 to 1,000 cases, displays the weekly incidence of the five most frequent reportable medical events among active duty service members over a 52-week period, from late June 2025 to late June 2026. The purpose of this chart is to monitor and compare the ongoing weekly surveillance trends of high-volume military health events. The data show that Chlamydia trachomatis infection is consistently the most frequently reported event, fluctuating between approximately 100 and 200 cases per week throughout the year. Gonorrhea represents the second-highest event, generally stable, between 20 and 50 cases weekly. Heat illness demonstrates a highly seasonal trend, peaking at nearly 100 cases per week during the summer months of 2025, dropping to near zero (including zero cases in week 4 of 2026) during the winter, and rising again as summer 2026 approaches. Norovirus and campylobacteriosis exhibit much lower and stable weekly baselines, typically remaining below 20 cases per week.

The DRSi requires the reporting of numerous gastrointestinal (GI) illnesses.1 In Q2 2026, the most frequently reported GI illnesses among U.S. ACSMs were norovirus, campylobacteriosis, and giardiasis. This is a change from the previous quarter, which involved a large cryptosporidiosis outbreak.

FIGURE 2. Selected Reportable Medical Events by Month, Active Component, U.S. Armed Forces, January 1, 2025–June 30, 2026 This multi-line comparative graph tracks monthly case reports of selected gastrointestinal illnesses—specifically norovirus, campylobacteriosis, and giardiasis—comparing monthly counts across the calendar years of 2025 and 2026. The purpose of the figure is to identify seasonal outbreaks and annual differences in gastrointestinal infections. The data demonstrate that Norovirus is the most common of these gastrointestinal events, exhibiting clear seasonal peaks in the winter and spring. In 2025, Norovirus reports peaked in January, at over 230 cases, and experienced a secondary peak in April at nearly 180 cases. In comparison, norovirus reports in 2026 were lower in April and May than the previous year, but rose slightly higher in June 2026, to around 60 cases. in contrast to norovirus, both campylobacteriosis and giardiasis maintain low, stable reporting levels throughout both years, consistently remaining below 50 cases per month, with campylobacteriosis showing only a minor increase during the summer months of 2025.

The number of reports for norovirus in DRSi were lower during April and May of 2026 than in their respective months in 2025, while the number of norovirus reports in June 2026 was slightly higher than June 2025. One norovirus outbreak report was submitted in June 2026 that included ACSMs. Additionally, campylobacteriosis and giardiasis reports in DRSi during Q2 2026 remained similar to the numbers of reports in the months of Q2 2025. One outbreak of campylobacteriosis was reported in May 2026 that affected ACSMs.

DCPH-A developed the Communicable Disease Toolkit to provide guidance for reporting RME cases and outbreaks to DRSi.2 Tools like investigation worksheets and case definition flowcharts are available in the Communicable Disease Toolkit for all RMEs, including reportable GI illnesses.

For questions about this report, please contact the Disease Epidemiology Branch at DCPH–Aberdeen. Email: dha.apg.pub-health-a.mbx.disease-epidemiologyprogram13@health.mil

References

  1. Armed Forces Health Surveillance Division. Armed Forces Reportable Medical Events. Accessed Aug. 26, 2026. https://health.mil/reference-center/publications/2022/11/01/armed-forces-reportable-medical-events-guidelines 
  2. Defense Health Agency-Public Health. Communicable Disease Toolkit. Accessed Aug. 26, 2026. https://ph.health.mil/topics/healthsurv/de/Pages/cdt.aspx

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