UCLA

Background: Monkeypox (MPX) virus is a zoonotic infection found in a variety of mammals, and infects humans with a smallpox-like illness. In the 30 years since the eradication of smallpox, monkeypox has emerged as the most severe orthopox infection occurring in humans. Most cases have been, and continue to be, reported in the Democratic Republic of Congo (DRC) where MPX is a reportable disease to the Integrated Disease Surveillance and Response (IDSR) unit. Despite the inclusion of MPX in the surveillance system, there may still be a number of limitations as to how accurately and how systematically this data has been collected, thus it is necessary to explore available data for trends in disease occurrence and reporting.

Methods: IDSR data consists of weekly reports on 15 diseases of epidemic potential or targeted for elimination or eradication. Case counts of all reportable diseases including MPX, acute flaccid paralysis (AFP), measles and tetanus reported via the IDSR unit to the 4th Direction in the Ministry of Health of the DRC were available from January 1st, 2001 through December 31st, 2013. The country is made up of over 10,000 public health facilities, which are required to report to the IDSR each week. Data available from the reports include: number of suspected cases and deaths, health zone, province, week reported, and numbers disaggregated by age category. A number of statistical methods were used to determine change in incidence, associations and comparisons with other diseases and lab reporting, and time series analysis. Additionally a model was created with parameters to determine the gaps in the system and to quantify the potential underreporting of suspected MPX cases.

Results: Between 2001 and 2013, three phases of the surveillance system were identified: the "implementation phase" (2001-2003), the "adjustment phase" (2004-2007), and the "stable phase" (2008-2013). Overall, there was an increase in suspected MPX cases reported via the IDSR. In total, 19,437 suspected cases and 336 suspected deaths (1.7% case fatality rate) were reported. During our study period, the mean number of reported MPX cases weekly was 42 (range: 0 -125). There were provincial differences in MPX reporting by week, however no significant trends were identified. Laboratory confirmed polio cases in a health zone had a negative impact on MPX, tetanus and measles reporting, but had a positive impact on AFP reporting. Health zones with confirmed cases of MPX had a positive association with MPX reporting, but a significant negative association with other diseases (AFP, measles and tetanus). We estimated that the possible under-reporting rate was 9.4 (range 5.0 to 15.2), with the majority (56%) of the cases being missed due to under-ascertainment of health services, and 8.3% lost due to inability to pay for services or visiting locations outside of he public health sector.

Discussion: Based on trends from 2008-2013, the "stable reporting phase", the increase in MPX is likely to be a true increase. The analyses indicate that while the system should be integrated (disease detection and confirmation) for all reportable diseases, that each component may only work within the specific diseases. Each missed case of a person with a suspected disease reduces the true incidence of that disease, leading to underestimates of disease burden. We estimate that only about 10% of the actual cases are making it to the national level. This could significantly limit the ability to detect emerging public health problems.