Pertussis.

Pertussis* 1. Brief description of the condition/disease Pertussis, a highly infectious, vaccine-preventable disease lasting many weeks, is caused by infection with Bordeiel(a pertussis. a bacillus first isolated in 1906 by Bordct and Gengou. Pertussis tvpically manifests as paroxysmal spasms of severe coughing. whooping. and post-tussive vomiting in cllildrcn The major complications, including hypoxia pneumonia. seizurcs, encephalopatlhy and malnutrition, are most common among infants and young children Pertussis is transmitted by direct contact witlh dis- charges rorn respiratorv mucous membranes of m- fected persons and by airborne dioplets. Like measles. it is highly contagious, with up to 90% of susceptible household cointacts developing clinical discase following exposuire to an index case. 2. Current global burden and rating within the overall burden of disease Pcrtussis results in high morbidity and mortality in many countries every year. Worldwide. 20654] cases were reported in 1994, and 80606 cases were reported in 1995. However. pertussis cases are sub- stantitally underreported in most countries. Wlhen this was taken into account. appioximately 39 mil- lion cases of pertussis and 3550()0 pcrtussts-related deaths occurred in 1995. Thle estinmated number of pertussis cases globally was similar to that of measles cases. The estimated numnber of pertussis-related deaths is one-third of the estimated number of measles-relaLed deaths and 100000 fcwei than deaths caused by neonatal tetanus. 3. Feasibility (biological) of elimination/eradication Pertussis elimination/eradication does not seem fea- sible for several reasons: whole-cell and acellular pertussis vaccines aie most cffective in preventing severe disease and may bave little impact on acqui- sition ot infection, preventing mild disease. and de- creasing transmiiission to otlher individuals: pertussis Contributed by Dalya Gurns, Peter Strebel and Melinda Wharton. Centers tor Disease Control and Prevention, Atlanta, GA, USA vaccines rcquLre multiple doses for protcction. hence they require a highly organized vaccine delivery sys- tem: immunity following vaccination wanes, and in the absence of booster vaccinations in older children and adults, susceptible adolescents and adults xill exist: the true burden of disease is not known be- cause underreporting is a major problenm in many countries: and pertussis is difficult to diagcnose par- ticularly during thie catarrhal stage when it is most contagious (therefore. even aggressive outbreak- control strategics are unilikely to contain it). Adequate herd immunilty to block pertussis transmission in a sustained fashion (>90%76 level of population immunity may be needed) may not be attainable even with 100% coverage. thc efficacy of cuirently available acellular and whole-cell vaccines is. at best 90%. Side-effects associatcd witb whole-cell pertussis vaccines are a major concern among health care pro- viders and parents. Altlhouglh new acellular pertussis vaccines cause fewer adverse reactions, they are sig- nificanitly nioie expcnsive, especially wlhen resources are limited in many countries. Because the patliogenesis of B. pertrissis and factors related to protectioin againist infecnon are not well known, development ot pertussis vaccines that are effective against infection and laboratory diagno- sis of pertussis are challenging. The followving factors faavour eliminationi/eradi- cation: humans are the only reservoir for B. pertussis; whole-cell and acellular pertussis vaccines are highly effective in preventing severe disease (the introduc- tion and widespread use of whole-cell pertussis vaccines, togethier wiLh improving socloeconomic conditions, has resulted in a marked decline in re- ported pertussis incidencc in many countnes): seasonality exists for pertussis epidemics, making tiansrmssion more vulnerable to interruption; anid long-term camrage is thought not to occur. 4. Estimated costs and benefits of elimination/eradication The estimnated costs to eliminate or eradicate pertussis are unlknown because an effective strategy has not yet been planned. Benefits of elimination or eradication are difficult to estimate in the absence of accurate data oni the true disease burden in all age groups in nmany countiries. However, eradica- tion would allow cessation of vaccination against pertussis. Buletin of Me World Heath Organization, 1998 76 (Suppl 21 137-138 137 Pertussis 5. Key strategies to accomplish the objectives Pertussis can be reduced among children vith imple- mentation of the EPI programme (>90% coverage with DPT3) and improved surveillance. Ilowever. elimination or eradication strategies have not been established because of limitations listed above in Section 3. 6. Research needs Research is needed to assess the true burden of in- fection in all age groups: develop and evaluate vaccines that are efficacious and sate for use among adolescents and adults: develop better diagnostic methods that are more sensitive and easy to pertorm and yield timely results; demonstrate local or re- gional elinmination and the effectiveness of outbreak- control measures; further laboratory research to understand the pathogenesis of B. pertmissis and host factors that are associated with protection against infection: and determine transmission patterns and identify critical factors involved in transmission to other persons through epidemiological studies. 7. Status of elimination/eradication efforts to date Implementation of EPI has achieved remarkable progress in decreasing pertussis incidence in many countries. However, the true burden of disease is difficult to estimate because of problems with diag- nosis and reporting of pertussis. 8. Principal challenges to elimination/eradication Challenges to eliminating/eradicating pertussis are as follows: current vacctnes may not prevent infec- tion and transmission to others, and immunity is not lifelong: cffectivec booster vaccination for adoles- cents and adults is not available: highly sensitive and specific diagnostic tests that are also easy and quick to perform are not available; knowledge of the true disease burden m all age groups is Jacking; and im- plementation of EPI is difficult. WHO Bulletn OMS Vol 76, Suppl 2 1998138