Case Study 1 | Statistical Analysis of Pertussis Cases OVERVIEW During 2004, a thirty-three-fold increase in pertussis (whooping cough) incidence in Southeastern Wisconsin triggered the activation of the unified command (see Appendix #1 for more details) of the public health consortium involving the fourteen local public health agencies in Milwaukee and Waukesha counties. BACKGROUND Pertussis (whooping cough) was endemic in Wisconsin for years, especially in the more populated southeastern region. Historically, pertussis accounted for approximately 170 cases annually in the state and caused small, isolated clusters in different regions. Prior to 2004, M and W counties (contiguously located within the southeastern region) averaged 34 and 15 pertussis cases per year, respectively. Though M and W counties were not affected, the state experienced a regional outbreak of pertussis cases in the northeastern portion in 2003; over 700 cases of pertussis were reported during this year, with the majority of cases related to the increased incidence in the northeastern region. Pertussis is an acute respiratory disease caused by the bacterium, Bordetella pertussis. Pertussis often begins insidiously with cold-like symptoms, including runny nose, possible low-grade fever and a mild, irritating cough that gradually becomes paroxysmal, usually within 1-2 weeks. The paroxysms are distinguished by a violent, explosive coughing that may interrupt breathing, eating and sleeping; vomiting may follow paroxysms. As they struggle to inhale air, patients may make a loud “whooping” sound characteristic of pertussis; infants and vaccinated individuals, however, may not have the typical whoop or cough paroxysm, making diagnosis difficult. 1,2 Spread through direct contact with respiratory droplets, pertussis is most contagious in the early stages of illness prior to developing paroxysms (generally the first two weeks). Communicability gradually wanes and becomes negligible in about three weeks, although the contagious period can be reduced to five days following effective antibiotic treatment. Persons with pertussis should be isolated from school, work or similar activities until they have completed at least five days of an appropriate antibiotic therapy. Appropriate antibiotics include a 5-day course of azithromycin, a 7-day course of clarithromycin, or a 14-day course of erythromycin or trimethoprim/sulfamethoxazole. Prophylaxis with an appropriate antibiotic is also recommended for close contacts (especially household contacts) of a case, to prevent or reduce illness severity. Pertussis is confirmed using polymerase chain reaction (PCR) or by laboratory culture of a nasal-pharyngeal swab specimen obtained during the early stages of illness. PCR has recently replaced culture as the test of choice for pertussis laboratory diagnosis because of its increased sensitivity, and the State Laboratory of Hygiene began using PCR for pertussis diagnosis in fall 2002. Vaccination with the diphtheria, tetanus and acellular pertussis vaccine (DTaP) is recommended for all persons under age seven who haven’t completed the five-dose vaccination series; the vaccine is not recommended for those over seven years because vaccine reactions are more frequent. Despite vaccination, the effectiveness of the vaccine is estimated to be only 80 percent in children receiving at least three doses. Additionally, recent research has shown that immunity begins to wane five to ten years following the last dose. CHRONOLOGY The start of 2004 brought increased pertussis rates in many areas of the state, including both M and W counties. Pertussis cases were reported to local health agencies at a steady rate throughout the first quarter of the year, with many local public health agencies reaching their average annual number of cases within the first few months of the year. Initially, public health practitioners believed the increased incidence was due in part to the 2003 outbreak in the northeastern portion of the state. January/February 2004 M County cases: 9 in January; 8 in February (17 cumulative total for year) W County cases: 4 in January; 6 in February (10 cumulative total for year) • State Health Officials within the Division of Public Health (DPH) sent 2003 provisional data on pertussis cases to local public health agencies stating, “… it appears that pertussis morbidity is beginning to subside…” March/April 2004 M County cases: 8 in March; 12 in April (37 cumulative total for year) W County cases: 4 in March; 10 in April (24 cumulative total for year) • Pertussis cases continued to increase and local public health agencies realized they were in the midst of a situation. • Clinical presentation was atypical from the “classic” pertussis symptoms, hampering accurate diagnosis. Most cases presented with prolonged minimal cough, with or without paroxysm or “whoop.” • The majority of cases occurred in adolescents and young adults who were fully immunized. • New cases required challenging cross-jurisdictional case management. May 2004 M County cases: 48 (85 cumulative total for year) W County cases: 21 (45 cumulative total for year) • Local Health Officers requested weekly or more frequent updates from DPH on pertussis activity in all regions and guidance on pertussis case management. • Questions arose as to whether DPH was monitoring incidence rates. • One local health agency instituted incident command (IC), to more effectively manage the pertussis epidemiological follow-up. • Other agencies informally changed their usual way of doing business, including reprioritization of daily functions and increased staff education, briefing, and updates. • Regional DPH personnel visited local health agencies to educate staff on pertussis. • DPH sent a letter to local health agencies on “significant increase in incidence of pertussis,” reiterating standard protocols as identified in DPH epidemiology manual. June 2004 M County cases: 57 (142 cumulative total for year) W County cases: 58 (103 cumulative total for year) • In absence of DPH guidelines, local public health agencies devised protocols to define and prioritize epidemiological follow-up. • DPH distributed 1999 CDC pertussis manual with updated state treatment guidelines. • DPH began posting positive laboratory results on the Health Alert Network (HAN) secure internet site after confidentiality concerns had been resolved. • Local public health agencies questioned reliability and validity of polymerase chain reaction (PCR) laboratory test. • Summer camp cases arose and frequently crossed jurisdictions. DPH sent 250 letters to camps with pertussis notification. • DPH sent letters to physicians on case definition, testing, and treatment. • An Antibiotic Resistant Network ongoing media campaign educated providers regarding appropriate antibiotic use. “Clinicians have worked hard to change their prescribing habits and to educate patients about the futility of antibiotics in the treatment of acute cough illnesses. The increased use of antibiotics caused by the pertussis outbreak is frustrating for clinicians who desire to both avoid antibiotic use for viral illness, and yet appropriately respond to a genuine public health need.” This contradicted public health protocols for pertussis prophylaxis, confusing providers about proper treatment guidelines and thereby increasing the difficulty of local public health agencies to assure appropriate prevention and control. • Local public health agencies needed to convey unified case management policies (case definition, close contact definition, testing, treatment, and isolation) to health care providers serving clients in multiple jurisdictions. July 2004 M County cases: 69 (211 cumulative total for year) W County cases: 87 (190 cumulative total for year) • A second local public health agency instituted IC. • PCR results displayed with regularity on the HAN. • DPH offered training on nasopharyngeal (NP) swabs to test for pertussis. • DPH assisted in obtaining test results from private clinical labs. • DPH instituted weekly pertussis

Local public health agencies needed to convey unified case management policies (case definition, close contact definition, testing, treatment, and isolation) to health care providers serving clients in multiple jurisdictions
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