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Delaware Health Alert Network #42

Sept 5, 2003 3:45 pm

Health Advisory

The Delaware Division of Public Health (DPH) is reporting the first confirmed human case of West Nile virus (WNV) during the 2003 season. DPH reminds health care providers that WNV is endemic in Delaware.

Patient Information

The patient is an adult woman who resides in Wilmington. The patient presented to the hospital on August 25 with a five-day history of fever, and a two-day history of headache and cough. She also had altered mental status, nausea and vomiting. The patient demonstrated West Nile IgM antibodies in both serum and cerebral spinal fluid. The patient currently remains hospitalized with West Nile encephalitis and is in stable condition.

Surveillance Update

The disease first appeared in Delaware birds and horses in 2000. Delaware's first confirmed human case of WNV occurred in 2002, and was not fatal. In 2002, 214 wild birds tested positive for WNV in Delaware, as did six mosquito pool samples and 24 horses. As of September 3, 2003, the DPH Laboratory has identified WNV in 80 wild birds submitted this year, as well as 11 sentinel chickens and 21 horses.

Nationally, as of September 4, 2003, 2667 human cases have been reported to the Centers for Disease Control and Prevention (CDC). Forty-three patients have died. In all of 2002, 4156 cases and 284 deaths were reported.

Clinical Suspicion

Most WNV infections (80 percent) are clinically inapparent. Approximately 20 percent of those infected develop a mild illness (West Nile fever), which includes sudden onset of fever and which may be accompanied by malaise, anorexia, headache, myalgia, nausea, vomiting, rash, lymphadenopathy, and eye pain. Symptoms generally last three to six days. Approximately 1 in 150 infections result in severe neurological disease, more commonly encephalitis than meningitis. The most important risk factor for developing severe neurological disease is advanced age. Neurologic presentations have included ataxia and extrapyramidal signs, optic neuritis, cranial nerve abnormalities, polyradiculitis, myelitis, and seizures. Several patients experienced severe muscle weakness and flaccid paralysis. Other associated symptoms include fever, weakness, and gastrointestinal symptoms. Myocarditis, pancreatitis, and fulminant hepatitis have also been described. The incubation period of WNV is thought to range from three to 14 days after the bite of an infected mosquito.

Diagnosis of WNV infection is based on a high index of clinical suspicion and obtaining specific laboratory tests. WNV should be strongly considered when unexplained encephalitis or meningitis occurs in summer or early fall. Local evidence of WNV enzootic activity or other human cases should further raise suspicion. Obtaining a recent travel history is also important.

Diagnostic Testing

The DPH Laboratory performs WNV testing for birds, horses and humans. Methods include antibody testing and confirmatory neutralization, as well as PCR, and culture. Detection of IgM antibody in human serum or spinal fluid is an effective method for diagnosing WNV infection. Serum should be collected within eight days of illness onset. False positive antibody results for WNV may occur in patients recently vaccinated for or infected with related flaviviruses (e.g. yellow fever, Japanese encephalitis, dengue). For submission of specimens call the virology laboratory at 302/653-2870.


Treatment is supportive, often involving hospitalization, intravenous fluids, respiratory support, and prevention of secondary infections for patients with severe disease.


To avoid mosquito bites and reduce the risk of infection, patients should be encouraged to:

  • Wear insect repellant containing less than 50% DEET for adults, less than 30% DEET for children;
  • Wear long-sleeved shirts and pants in mosquito-infested areas;
  • Avoid peak mosquito activity during dusk, evening or early morning;
  • Drain or remove items that collect water and provide mosquito-breeding habitat, such as buckets, rain barrels, old tires, blocked rain gutters and unused swimming pools.

Additional Resources

  • For questions about WNV in humans, and to report suspected human cases, call DPH at 888-295-5156.
  • To report sick or dead wild birds, call Mosquito Control between 8 a.m. and 4:30 p.m. in New Castle County at (302) 323-4492, and in Kent or Sussex counties, call (302) 422-1512.
  • For general information about mosquito control, contact DNREC at (302) 739-3493.
  • For questions about animal health, call the Department of Agriculture at 1-800-282-8685 between 8 a.m. and 4:30 p.m., or leave a message after-hours.
  • The Center's for Disease Control and Prevention's WNV website is:

Categories of Health Alert messages:

  • Health Alert: Conveys the highest level of importance; warrants immediate action or attention.
  • Health Advisory: Provides important information for a specific incident or situation; may not require immediate action.
  • Health Update: Provides updated information regarding an incident or situation; unlikely to require immediate action.
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