Can active surveillance provide a rapid response to an emerging child health issue? The melamine example

In mid-September 2008, the federal government became aware of an outbreak of renal disease (renal stones and/or acute renal failure) in very young children in China, associated with consumption of powdered infant formula that was adulterated with melamine. Thousands of children in China were hospitalized, and several died (1). Melamine contamination was also found in other Chinese products that had a milk component, such as candies and coffee drinks.

Some Chinese milk-derived products sold in Canada were found to contain low levels of melamine and were recalled from the market (2). Infant formula manufactured in China is not approved for sale in Canada, and the manufacturers of infant formula sold in Canada do not use any milk ingredients originating in China. Therefore, the likelihood of Canadian infants being exposed to the formula that was affecting so many children in China was very low. Nevertheless, in light of patterns of international travel, adoption and immigration, there was a possibility that infants in Canada might be affected. Working in concert with Health Canada and the Canadian Food Inspection Agency, the Public Health Agency of Canada (PHAC) provided information for health care professionals and the public on this issue (3,4). The PHAC also endeavoured to determine whether there were cases of renal illness in Canadian children that may have been caused by the milk formula contamination in China.

The data in national hospitalization databases are not timely enough to meet this type of health surveillance need. Therefore, as a first step in the identification of possible melamine-associated illness in Canada, the PHAC asked paediatric hospital emergency departments, Paediatric Chairs, Paediatric Surgical Chiefs of Canada and members of the Canadian Association of Paediatric Health Centres to report any recent increases or unusual patterns of renal illness, in particular urinary calculi or renal failure, in infants or very young children seen in their institutions. The PHAC followed this inquiry, which had no positive reports, with a request to the Canadian Paediatric Surveillance Program (CPSP) to conduct an emergency one-time survey on the issue. It is this process that is the subject of the present article.

CPSP SURVEILLANCE PROCESS

The CPSP, established in 1996, conducts active surveillance by consulting with more than 2400 paediatricians and paediatric subspecialists monthly to assess low-frequency, high-impact conditions affecting children and youth (5). The program collects valuable national epidemiological data and contributes to the International Network of Paediatric Surveillance Units (6).

To assess whether Canadian children were presenting with renal stones and/or acute renal failure that may have been caused by melamine contamination, the CPSP initiated a one-time survey (Figure 1) adapted from, and in collaboration with, the New Zealand Paediatric Surveillance Unit (NZPSU), which also undertook such a survey following a similar request from their government. The results of the NZPSU survey will be published elsewhere. Before dissemination, the Canadian survey questions were reviewed by members of the CPSP steering committee – a broad group of paediatricians and other professionals with expertise in paediatric surveillance.

Figure 1).

The CPSP one-time survey on renal stones and/or unexplained acute renal failure in infants

The 2475 CPSP participants were asked whether, over the past 12 months, parents had consulted with them about possible milk product contamination. They were also asked whether they had recently seen any infants (younger than one year of age) with renal stones and/or unexplained acute renal failure. If the answer was affirmative for the second question, participants then completed the next part of the survey, which consisted of a short clinical questionnaire.

RESULTS OF THE CPSP

The response rate was 42%. No cases of melamine-associated renal disease were reported by the 1153 respondents. Twelve cases of renal stones were reported, and one of these cases also had acute renal failure. The majority of children had urinary tract infections (n=7). Other associated factors included hydronephrosis, diuretic therapy, hyperparathyroidism and prematurity. Hypercalciuria was present in seven cases and hyperoxaluria in one case. Interestingly, almost 10% of respondents mentioned that parental concerns about contaminated milk products were voiced to them, especially to those who worked in international adoption clinics.

DISCUSSION

The melamine example demonstrates how a national paediatric surveillance program can be mobilized quickly to conduct enhanced surveillance in the event of an emerging public health concern in children.

Within 10 working days of being asked by the PHAC to undertake this task, the CPSP sent out a one-time survey to its 2475 participants. This was performed in collaboration, first, with the NZPSU, and second, with the PHAC staff who rapidly entered and analyzed the data. The results were available three weeks after the survey was initiated.

In this situation, the CPSP was the appropriate tool for gathering the required information. First, as demonstrated by the response rate, the paediatricians who report every month are willing to participate in emergency surveillance. Second, because of the nature of the illness (rare, unusual and complex), it is highly likely that a paediatrician would have seen these cases. Third, the data collected, which included clinical information, were unique to this surveillance program – national hospitalization data are not timely enough, and laboratories, in this instance, would not be a feasible data source.

At first glance, the response rate of 42% may seem low. However, a review (7) of 321 distinct published physician mail surveys showed a mean response rate of 54%. Also, the CPSP survey was performed without incentives and without reminders. Furthermore, many of the 2475 program participants were paediatric subspecialists (eg, adolescent medicine, neurology) who would not be seeing cases of renal stones and/or unexplained acute renal failure in infants, and have not responded to the present one-time survey.

The melamine example has demonstrated the potential for the PHAC and the Canadian Paediatric Society to work together through the CPSP to carry out national emergency surveillance of rare conditions quickly and inexpensively, to inform public health responses to disease management and prevention. This surveillance program has the advantage of being well established, with a national network of diligent, frontline paediatricians and an international network of paediatric surveillance units. The CPSP currently uses regular mail to send out and receive survey results. The program is in the process of considering electronic reporting, which has the potential to improve survey response rate and speed of responses.