Norovirus outbreak aboard USNS Mercy during Pacific Partnership 2015 Phillip R. Perrinez1, MD, PhD; Mari K. Brown2, MPH, MS; Drake H. Tilley3, MD, MPH&TM

1Departments of Internal Medicine and 3Infectious Diseases, Naval Medical Center, San Diego, CA 92134 2Navy Environmental and Preventive Medicine Unit Five, San Diego, CA, 92136

INTRODUCTION USNS Mercy is a U.S. Navy hospital ship routinely deployed to Southeast Asia to provide humanitarian assistance and disaster response support. Norovirus (NoV) infection is characterized by acute onset of nausea, vomiting, abdominal cramping, and non-bloody diarrhea. Both hospitals and ships are prone to NoV outbreaks. Attack rates (α) in excess of 40% have been reported aboard military and civilian ships. A NoV outbreak was detected aboard USNS MERCY while in Roxas City, Philippines in July 2015. This is the first known shipboard NoV outbreak where real-time molecular surveillance testing was used to facilitate detection and guide control measures.

Noroviruses • Single-stranded RNA viruses Clinical Features • Acute gastroenteritis - Non-bloody diarrhea, nausea/vomiting, abdominal cramps (low-grade fever + body aches)

• Incubation (12-48 hrs); Illness duration (24-72 hrs) Transmission (extremely contagious) • Person-person, foodborne, waterborne - Fecal-oral, aerosolized vomitus, fomites, contaminated surfaces

• Infectious dose: 18 viral particles • Viral shedding (stool): Peak 2-5 days following infection (100x 109 copies/gm)

METHODS Syndromic diarrhea surveillance was performed during the Pacific Partnership mission from 17MAY2015 to 29SEP2015 and included all personnel that presented to sick call with the chief complaint of nausea, vomiting, or diarrhea. Multiplex PCR testing (FilmArray® system by Biomerieux) was used to identify infectious agents when increased rates of diarrhea were observed. Basic demographic and clinical data were collected prospectively as part of the outbreak investigation. Early, aggressive control measures including isolation, hand washing campaigns, screening of food handlers, and decontamination of high traffic areas were implemented.

RESULTS

A NoV outbreak was detected from 17JUL2015 to 03AUG2015. The baseline incidence of GI-related illness was 0.4% (σ ± 0.3%). Patients that had diarrhea and nausea/vomiting were included as cases. A total of 72 cases were identified. The average census during this period was 1023 (αo = 7.0%). 5/6 stool samples tested were positive for NoV. Of the cases, 85% of patients presented to medical attention within the first 48 hours after symptom onset. 36% of cases were identified from a single berthing space (αb = 25%), and 69% of all cases were from berthing spaces connected by a common ladderwell. Individuals who experienced the onset of symptoms within the first 72 hours were more likely to have consumed raw oysters and/or shellfish [OR 7.18; 95% CI 3.13-16.5].

CONCLUSIONS Hospital ships are particularly vulnerable to diarrheal outbreaks during humanitarian or disaster relief missions that can, in turn, impact mission readiness and capacity. Implementation of a vigilant surveillance system in coordination with point-of-care molecular diagnostics allowed for early detection and aggressive infection control measures to mitigate transmission and limit the infectious burden during a NoV outbreak aboard USNS Mercy.

REFERENCES 1. Corwin, A. L., Soderquist, R., Edwards, M., White, A., Beecham, J., Mills, P., Oyofo, B.

(1999). Shipboard impact of a probable Norwalk virus outbreak from coastal Japan. The American journal of tropical medicine and hygiene, 61(6), 898-903.

2. Centers for Disease Control and Prevention (2011). Updated Norovirus Outbreak Management and Disease Prevention Guidelines. MMWR 60(3), 1-20.

3. Centers for Disease Control and Prevention. Vessel Sanitation Program. http://www.cdc.gov/nceh/vsp/default.htm, 14 Jan 2016.

4. Gonzaga, V. E., Ramos, M., Maves, R. C., Freeman, R., & Montgomery, J. M. (2011). Concurrent outbreak of norovirus genotype I and enterotoxigenic Escherichia coli on a US Navy ship following a visit to Lima, Peru. PloS one, 6(6), e20822.

5. Navy and Marine Corps Public Health Center (2011). Norovirus Illness Prevention & Control Guidance for the U.S. Fleet.

Case Definition

Symptom Number (n) Frequency (%)

Diarrhea 65 90 Nausea 55 76 Vomiting 49 68 Abdominal Cramping/Pain 38 53 Body Aches 32 44 Fever 16 22 Cases Presenting ≤ 72 hrs Index

Cases Presenting > 72 hrs Nosocomial

Disclaimer: The views expressed are those of the authors and do not reflect the official policy or position of the Department of the Navy, the Department of Defense, or the United States Government.

Pacific Partnership 2015

USNS Mercy (T-AH 19)

USNS Mercy (T-AH 19) is a U.S. Naval hospital ship routinely deployed to South-East Asia to provide humanitarian assistance and disaster response support as part of Pacific Partnership.

Mission: U.S. Pacific Fleet annual humanitarian and civic assistance exercise aimed at strengthening international relationships with partner and host nations in the Asia-Pacific region.

Partner Nations: United States, Australia, Japan, Malaysia, New Zealand, Canada, Fiji, Timor-Leste, Singapore, Republic of Korea, France.

Host Nations: Fiji, Papua New Guinea, Philippines, Vietnam.

Statistics: 1,200 total personnel. 649 surgeries performed on board. Provided medical/dental care for > 16,000 patients at community health engagements (approximately 5200 in Philippines).

CDC Vessel Sanitation Program (VSP)

Applies to cruise ships that: • Visit both foreign and U.S. ports. • Carry 13 or more passengers.

When does CDC conduct an investigation? • If ≥ 3% of passengers or crew experience GI illness, OR if an unusual GI illness pattern or characteristic is identified.

What is an Outbreak?

Definition: Occurrence of a medical condition that exceeds the baseline/expected rate within a specific place or group over time.

What is an Outbreak Investigation?

Objectives: 1. Determine the magnitude of illness aboard the ship. 2. Identify the pathogen causing the illness. 3. Identify risk factors associated with the illness. 4. Formulate control measures to prevent or stop the spread of illness.

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Epidemic Curve

Liberty Call

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Date

Rate of GI Illness Observed (17 May – 05 Aug 2015) Baseline Incidence (3-day)

JUNE JULY AUGUST MAY

HAWAII 25-27 MAY

FIJI 07-18 JUNE

PNG 27 JUNE-10 JULY

ROXAS CITY, PI 18 JUL-03 AUG

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A B C D E F G H MO FO CPO

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Berthing

Case Distribution αP = 9.2% 69% of cases

αMO = 5.5% αFO = 3.4% αA/B = 4.1% αCDEF = 3.7%

αH = 25% 36% of cases

Date # Cases Intervention

20-Jul 0

21-Jul 4 I • Stool PCR (+) for NoV.

22-Jul 8 II • Berthing heads and galley disinfected using

virucidal agent.

23-Jul 12 III

• NoV outbreak identified. • Berthing heads disinfected. • Crew education on risk for nosocomial

transmission. (Hand washing). • Crew encouraged to seek medical attention if

symptomatic.

24-Jul 11 IV • Quarantine initiated (symptomatic). • Discontinued self-service food items.

25-Jul 6 V • NoV brief added to closed-circuit TV (continuous

loop).

26-Jul 6 VI • Reinforced disinfection guidelines.

27-Jul 5

28-Jul 7

29-Jul 5 VII • Ladderwells, passage ways, common areas

disinfected.

30-Jul 3

31-Jul 1

01-Aug 0 VIII • Quarantine lifted.

**OUTBREAK**

Arrive Roxas City

Average Attack Rate (%)

Passenger Crew

7.0 1.5

Max 21 6.4

Min 3.2 0.2

σ 3.4 1.1

Exposure/Activity All Cases (n = 72) Controls (n = 180) OR (95% CI) p

Bay Bay Beach 29 141 0.19 (0.11-0.33) < 0.001

Coco Veranda 16 81 0.35 (0.19-0.65) < 0.001

Oysters/Shellfish 16 22 2.05 (1.01-4.15) 0.05

Galley/MRE Only 9 2 12.7 (3.65-44.3) < 0.001

Exposure/Activity Index (n = 24) Controls (n = 180) OR (95% CI) p

Bay Bay Beach 17 141 0.67 (0.26-1.73) 0.44

Coco Veranda 10 81 0.87 (0.37-2.07) 0.83

Oysters/Shellfish 12 22 7.18 (3.13-16. 5) < 0.001

Galley/MRE Only 1 2 3.87 (0.40-37.7) 0.31

Exposure/Activity Nosocomial (n = 48) Controls (n = 180) OR (95% CI) p

Bay Bay Beach 12 141 0.09 (0.05-0.18) < 0.001

Coco Veranda 6 81 0.17 (0.08-0.40) < 0.001

Oysters/Shellfish 4 22 0.65 (0.21-1.98) 0.61

Galley/MRE Only 8 2 17.8 (5.31-59.7) < 0.001

USNS Mercy (Roxas City)

Average Census 1023

No. Cases 72

No. Controls 180

Attack Rate (αo) 7.0%

Demographics Case Control

Gender

Male 59 128

Female 13 52

Mean Age (yrs) [σ] 30 [7.3] 30 [9.3]

Survey of 50 NoV outbreaks aboard international cruise ships (May 2011 – Nov 2015)