“Right now, we are hard at work doing what we do best — protecting people's health whenever, wherever and however we are needed. For that I, and people around the world, are most grateful.” This is what Julie Gerberding, the director of the US Centers for Disease Control and Prevention (CDC), wrote in an e-mail message to employees last week; it was subsequently reprinted in the Atlanta Journal-Constitution.

Many of us do indeed have cause to be grateful for the work of the CDC. The federal agency, which started in 1946 as a small office to investigate malaria, now has around 9,000 staff and is dedicated to improving all aspects of public health in the United States. When members of the public are concerned about what vaccinations to give their children, they turn to the CDC for advice. When local health departments need guidance on the spread of HIV, they too look to the Atlanta-based agency.

Outside the United States, the CDC enjoys a hard-won reputation for its knowledge of infectious disease. Take, for example, its unparalleled 121 Cities programme for monitoring influenza, as part of which epidemiologists collect weekly figures on the number of influenza deaths from (as it happens) 122 US metropolitan areas. The programme, which can highlight a particularly pernicious flu season at its outset, is unmatched elsewhere in the world.

But some of the people who respect and rely on the CDC are now expressing worries about its own state of health. Some of those concerns are being expressed at the very roots of the agency itself, by the dedicated public-health workers on whose reputation it was built. It was the Atlanta Journal-Constitution's reporting of these concerns that prompted Gerberding's e-mail retort.

The complainants allege that good science at the agency is being hampered by bureaucracy and mismanagement. The problems have arisen in part as the result of a reorganization instigated by Gerberding in 2003, and some officials contend that they are being exacerbated by the Bush administration's efforts to exert political influence over the CDC. Some very senior people are leaving; others say they are staying only until they can collect a pension (see page 250).

When five former directors of the CDC feel compelled to intervene, as they did last year, it is time for outsiders to pay attention.

Some of these complaints may well have been provoked by any kind of organizational revamp. But when five former directors of the CDC feel compelled to intervene, as they did in a letter sent to Gerberding last year, it is time for outsiders to pay attention.

The CDC's role in helping to assure public health has never been more important. Emerging infectious diseases such as SARS and avian influenza demand a rapid response, and epidemics of HIV and tuberculosis show few signs of abating. Obesity, heart disease and cancer end too many lives prematurely and demand authoritative and assertive management.

The CDC is not the only globally significant public-health organization whose performance is currently under scrutiny. Later this year, the World Health Organization (WHO) is due to elect a director-general to succeed Lee Jong-wook, who died this summer. It is critically important that the WHO chooses a leader with the political and administrative skills needed to make the organization an even more effective player in addressing global public-health issues. Unfortunately, given the intrigue that often surrounds such contests, close observers of the WHO have scant grounds for optimism that this election will yield such a leader.

The Senate Finance Committee is already looking into alleged staff morale problems at the CDC, as well as the agency's use of funds that it has been asked to spend to counter bioterrorism. It is the duty of congressional committees to ensure that the agency and its money are being competently managed. Scientific bodies such as the National Academies could also be asked to play a role in monitoring the CDC's well-being. They should welcome any opportunity to do so, to help ensure that the agency maintains its proud tradition as an effective champion of public health, at home and abroad.